[1] The act criminalises speech with "seditious tendency", including that which would "bring into hatred or contempt or to excite disaffection against" the government or engender "feelings of ill-will and hostility between different races".

After the May 13 Incident, when racial riots in the capital of Kuala Lumpur led to at least 200 deaths, the government amended the Constitution to expand the scope of limitations on freedom of speech.

[4] In Britain, the laws were condemned, with The Times of London stating they would "preserve as immutable the feudal system dominating Malay society" by "giving this archaic body of petty constitutional monarchs incredible blocking power"; the move was cast as hypocritical, given that Deputy Prime Minister Tun Abdul Razak had spoken of "the full realization that important matters must no longer be swept under the carpet..."[5] There have been several challenges to the constitutionality of the Sedition Act.

[6] The Sedition Act would be unconstitutional, as the Constitution guarantees freedom of speech, without Article 10(2) of the Constitution, which permits Parliament to enact "such restrictions as it deems necessary or expedient in the interest of the security of the Federation or any part thereof, friendly relations with other countries, public order or morality and restrictions designed to protect the privileges of Parliament or of any Legislative Assembly or to provide against contempt of court, defamation, or incitement to any offence".

The editor for the opposition was also charged with sedition for alleging a government conspiracy against Anwar Ibrahim, a former Deputy Prime Minister, had led to his political downfall.

Lim Guan Eng, a former Member of Parliament from the opposing party DAP, had also been found guilty of sedition in 1998 for accusing the Attorney General of failing to properly handle a case where the Chief Minister of Malacca had been charged with statutory rape of a schoolgirl.

That same year, the online publication Malaysiakini was temporarily shut down under the Sedition Act after it published a letter criticising Malay special rights and compared the Youth wing of a government party to the Ku Klux Klan.

[3] Previously in 1978, the Sedition Act had been invoked in another case of educational policy, when Mark Koding argued in Parliament that the government ought to close down Chinese and Tamil vernacular schools.

[9] In November 2020, a student group at the University of Malaya called the Association of New Youth (UMANY) was investigated under the Sedition Act after posting an article on Facebook titled “Yang di-Pertuan Agong should not intervene in national affairs".

Sharp criticism followed the passing of the law from the top United Nations human rights official Zeid Ra'ad Al Hussein.

Some people, including an article published by The Star, have claimed that these amendments were made with current forms of dissent in mind, such as critical postings on social media.

If the publication is considered to be seditious, "the Sessions Court Judge shall make an order directing an officer authorized under the Communications and Multimedia Act 1998 [Act 588] to prevent access to such publication.” Zahid Hamidi stated that these amendments were made because the changing political landscape where people can easily spread seditious remarks through the Internet - "Last time, there was no Internet and non-verbal communication over social media.

[15] Human rights advocates such from organizations such as Amnesty International and Article 19 have made consistent claims that the Sedition Act is an attack on the freedom of speech in Malaysia.

[13][20] Critics argue that the definition of sedition in the Act is vague or overly "broad and inflexible",[21][13] which could "potentially lead to an "overreach" or an "abusive application of the law".