Praise be to Allaah.

Firstly: 

Promulgating man-made laws that are contrary to the rulings of Allah and His Messenger concerning matters of blood, honour and wealth, is an act of major kufr which puts one beyond the pale of Islam. There is no doubt whatsoever concerning that, and there is no difference of opinion concerning it among the Muslim scholars. Promulgating such laws is competing with Allah, may He be exalted, in His rule and is going against Him in His laws. Allah says (interpretation of the meaning): "Or have they partners with Allaah (false gods) who have instituted for them a religion which Allaah has not ordained?" [al-Shoora 42:21]. 

And Allah says concerning obedience to one who permits dead meat (interpretation of the meaning):

"Eat not (O believers) of that (meat) on which Allaah's Name has not been pronounced (at the time of the slaughtering of the animal), for sure it is Fisq (a sin and disobedience of Allaah). And certainly, the Shayaateen (devils) do inspire their friends (from mankind) to dispute with you, and if you obey them [by making Al‑Maytah (a dead animal) legal by eating it], then you would indeed be Mushrikoon (polytheists); [because they (devils and their friends) made lawful to you to eat that which Allaah has made unlawful to eat and you obeyed them by considering it lawful to eat, and by doing so you worshipped them; and to worship others besides Allaah is polytheism]"

[al-An‘aam 6:121]. 

And Allah says (interpretation of the meaning):

"Have you not seen those (hypocrites) who claim that they believe in that which has been sent down to you, and that which was sent down before you, and they wish to go for judgement (in their disputes) to the Taaghoot (false judges) while they have been ordered to reject them. But Shaytaan (Satan) wishes to lead them far astray.

61. And when it is said to them: ‘Come to what Allaah has sent down and to the Messenger (Muhammad صلى الله عليه وسلم),' you (Muhammad صلى الله عليه وسلم) see the hypocrites turn away from you (Muhammad صلى الله عليه وسلم) with aversion"

[al-Nisa' 4:60-61]. 

If this is the ruling of Allah concerning the one who wants to refer for judgement to false judges, then how about the false judge himself who promulgates laws instead of Allah. 

How can legislation that is contrary to the laws of Allah not be kufr, when it inevitably implies permitting that which is forbidden and forbidding that which is permitted, or giving the legislators the right to do that, so they have the right to permit whatever they want and to forbid whatever they want; whatever the majority agrees upon must be carried out and the one who goes against it is punished and criminalised. This is the ultimate kufr. 

Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said: If a person regards as permissible that on which there is scholarly consensus that it is forbidden, or regards as forbidden that on which there is scholarly consensus that it is permitted, or he alters a law on which there is consensus, then he is a kaafir and apostate, according to the consensus of the fuqaha'.

End quote from Majmoo‘ al-Fataawa, 3/267 

Ibn Katheer (may Allah have mercy on him) said: The one who forsakes the law that was revealed to Muhammad ibn ‘Abd-Allah, the Seal of the Prophets (blessings and peace of Allah be upon him) and refers for judgement to any other law that has been abrogated, has committed an act of kufr, so how about the one who refers for judgement to al-Yaasa and gives it precedence? The one who does that is a kaafir according to the consensus of the Muslims.

End quote from al-Bidaayah wa'l-Nihaayah, 13/139. 

Al-Yaasa (also known as al-Yaasiq) refers to the laws of the Tatar Genghis Khan, who forced the people to refer to them for judgement.

Undoubtedly the one who promulgates laws himself commits a greater act of kufr and is more misguided than one who refers to them for judgement. 

Al-‘Allaamah Muhammad al-Ameen al-Shanqeeti (may Allah have mercy on him) said: From verses such as that in which Allah says (interpretation of the meaning) "and He makes none to share in His Decision and His Rule" [al-Kahf 18:26], it may be understood that the followers of those who promulgate laws other than those which Allah has ordained are associating others with Allah (shirk). This understanding is explained clearly in other verses, such as the verse which speaks of those who follow the laws of the Shaytaan in permitting dead meat, claiming that it has been killed by Allah [and thus should be permitted]:

"Eat not (O believers) of that (meat) on which Allaah's Name has not been pronounced (at the time of the slaughtering of the animal), for sure it is Fisq (a sin and disobedience of Allaah). And certainly, the Shayaateen (devils) do inspire their friends (from mankind) to dispute with you, and if you obey them [by making Al‑Maytah (a dead animal) legal by eating it], then you would indeed be Mushrikoon (polytheists)"

[al-An‘aam 6:121]. 

Here Allah clearly states that they would be mushrikoon by obeying them. This is associating others with Allah in terms of obedience and following laws that are contrary to that which Allah has ordained -- which is what is meant by worshipping the Shaytaan in the verse in which Allah says (interpretation of the meaning):

"Did I not command you, O Children of Adam, that you should not worship Shaytaan (Satan). Verily, he is a plain enemy to you.

61. And that you should worship Me [Alone Islamic Monotheism, and set up not rivals, associate‑gods with Me]. That is the Straight Path"

[Ya-Seen 36:60-61]. 

And Allah tells us that His Prophet Ibraaheem said (interpretation of the meaning):

" ‘O my father! Worship not Shaitân (Satan). Verily, Shaitân (Satan) has been a rebel against the Most Gracious (Allaah)'"

[Maryam 19:44]. 

And Allah says (interpretation of the meaning):

"They (all those who worship others than Allaah) invoke nothing but female deities besides Him (Allaah), and they invoke nothing but Shaytaan (Satan), a persistent rebel!"

[al-Nisa' 4:117], i.e., they do not worship anything but a devil, i.e., by following his laws. Hence Allah calls those whom they obey in the sins that they made attractive to them "partners", as in the verse (interpretation of the meaning) "And so to many of the Mushrikoon (polytheists) their (Allaah's so‑called) ‘partners' have made fair-seeming the killing of their children, in order to lead them to their own destruction and cause confusion in their religion" [al-An ‘am 6:137]. The Prophet (blessings and peace of Allah be upon him) explained this to ‘Adiyy ibn Haatim (may Allah be pleased with him) when he asked him about the verse in which Allah says (interpretation of the meaning): "They (Jews and Christians) took their rabbis and their monks to be their lords besides Allaah" [al-Tawbah 9:31]. He explained that they permitted to them that which Allah has forbidden and they forbade to them that which Allah has permitted, and they [the people] followed them in that; that is how they took them as lords. 

One of the clearest proofs concerning that is the fact that in Soorat al-Nisa', Allah, may He be glorified and exalted, mentioned those who want to refer for judgement to something other than the laws prescribed by Him and wonders at their claim to be believers, because their claim to be believers even though they want to refer for judgement to false judges shows that they have reached a level of lying which is astounding. That is what Allah says (interpretation of the meaning):

"Have you not seen those (hypocrites) who claim that they believe in that which has been sent down to you, and that which was sent down before you, and they wish to go for judgement (in their disputes) to the Taaghoot (false judges) while they have been ordered to reject them. But Shaytaan (Satan) wishes to lead them far astray"

[al-Nisa' 4:60]. 

From the divinely revealed texts that we have quoted, it becomes very clear to everyone that with regard to those who follow man-made laws promulgated by the Shaytaan on the lips of his supporters which are contrary to that which Allah has prescribed on the lips of His Messengers (blessings and peace of Allah be upon them), there is no doubt that they are kaafirs and mushriks, except for the one whom Allah has blinded to the light of Revelation and left to go astray.  

And he said: 

As for the legal system that is contrary to the laws prescribed by the Creator of heaven and earth, ruling according to it constitutes disbelief in the Creator of heaven and earth, such as the claim that giving precedence to the male over the female in inheritance is not fair and it is necessary to make them equal in inheritance, and the claim that plural marriage is unjust, or that divorce is unfair to the woman, and that stoning, cutting off the hand and so on are barbaric acts that should not be done to people, and so on. 

Making this kind of system rule the lives of people in society and their wealth, honour, lineage, reason and religion, is disbelief in the Creator of heaven and earth and a transgression against the divine system prescribed by the One Who created all things and Who knows best what is in their best interests; may He be glorified and exalted far above having any lawgiver besides Him.

"Or have they partners with Allaah (false gods) who have instituted for them a religion which Allaah has not ordained?"

[al-Shoora 42:21]

"Say (O Muhammad to these polytheists): ‘Tell me, what provision Allaah has sent down to you! And you have made of it lawful and unlawful.' Say (O Muhammad): ‘Has Allaah permitted you (to do so), or do you invent a lie against Allaah?'"

[Yoonus 10:59]

"Say: ‘Verily, those who invent a lie against Allaah will never be successful'"

[Yoonus 10:69]. 

End quote from Adwa' al-Bayaan, commentary on the verse (interpretation of the meaning): "and He makes none to share in His Decision and His Rule" [al-Kahf 18:26]. 

See also the answer to question no. 11309 and 974. 

Secondly: 

What is well established and known of the view of Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) is that he clearly stated that promulgating laws that are contrary to what Allah has revealed constitutes major kufr. He mentioned that in several places in his books, such as Sharh Kitaab al-Tawheed, Sharh al-Usool al-Thalaathah, Sharh al-Siyaasah al-Shara‘iyyah, and his fatwas which have been published in al-‘Aqeedah and Liqaa'aat al-Baab al-Maftooh. All his comments on these subjects are consistent and point to the same conclusion, which is that legislating and promulgating laws that are contrary to the sharee‘ah of Allah constitutes major kufr. As for the one who rules according to something other than that which Allah has revealed, he may be a disbeliever or a wrongdoer or an evildoer according to the crime that he has committed. We do not know of any opinion of the Shaykh concerning this matter, in which he suggested that this promulgation of laws is minor kufr. If the Shaykh had any other opinion, it would have widely known, and the Shaykh would have clearly recanted his first opinion, and striven to prevent it being published. Whoever thinks that any of the scholars would recant something that it became clear to him was wrong, then would continue to publicise the mistaken opinion until he died, without denouncing it or instructing that it be erased, has thought badly of him and has impugned his religious commitment and honesty, because it is not permissible to publicise a false opinion or to keep quiet about it, especially if it has to do with an important matter such as this. 

Among the things that he (may Allah have mercy on him) said concerning this matter is what appears in Sharh al-Usool al-Thalaathah, where he said: Whoever does not rule in accordance with that which Allah has revealed because he thinks little of it or looks down on it or believes that something else is better than it and more beneficial to people or is equal to it, is a kaafir whose kufr puts him beyond the pale of Islam. That includes those who promulgate laws for people that are contrary to Islamic laws, to be a system that the people follow. They only promulgate those laws that are contrary to Islamic laws because they believe that they are better and more beneficial for people, because it is known on the basis of reason and sound human nature that no one turns away from one path to a different path unless he believes that what he has turned to is better and what he has turned away from is lacking. 

End quote from Majma‘ al-Fatawa wa Rasaa'il al-Shaykh Ibn ‘Uthaymeen, 6/161. 

And Allah knows best.