PHNOM PENH, CAMBODIA: Cambodia's National Assembly approved a controversial draft law Monday that critics say gives authorities sweeping powers to crack down on civil society groups that challenge the government.

Riot police set up a barricade around the lower house of parliament to hold back hundreds of protesters there and opposition party lawmakers boycotted the vote entirely.

The Law on Associations and Non-Governmental Organisations tightly regulates all non-governmental organisations in the country and grants the government sweeping powers to clamp down on civil society activities it deems to be a threat to national security.

A final draft of the bill has not been released to the public, another aspect that has drawn criticism. But according to a copy obtained from lawmakers, it states that local and foreign non-governmental organisations must register with the government, and that all NGOs must be politically neutral. It also gives the government unchecked power to block registrations and dissolve groups in the name of national security.

The law is the first of four in the pipeline that critics say are designed to further restrict social freedoms in Cambodia, which has been ruled since 1985 by Prime Minister Hun Sen, an autocrat with little tolerance for dissent.

The opposition Cambodian National Rescue Party issued a statement ahead of the session saying it "deeply regretted" that the bill did not include its input or any input from the non-governmental groups it aims to restrict. The opposition's 55 lawmakers boycotted Monday's debate.

All 68 lawmakers from the ruling Cambodian People's Party voted unanimously to adopt the bill, an expected outcome in the 123-seat lower house, where a simple majority was enough for the vote to pass. The bill still needs to clear the Senate before becoming law, a step considered a formality in Cambodia.

The European Parliament adopted a resolution last week calling on the Cambodian government to withdraw the vote, warning that $700 million in development aid could hang in the balance, and Amnesty International has condemned the law as repressive.

"This will create an atmosphere of intimidation and self-censorship among NGOs who will realise that the Cambodian government will be able to shut them down at any time," said Phil Robertson, the deputy Asian director of Human Rights Watch.

The US ambassador to Cambodia, William Todd, also criticised the lack of transparency, urging ruling party lawmakers to publicly release a copy of the draft law to allow a full public debate. In 2014, the US gave roughly $75 million in aid to Cambodia.

Other laws in the pipeline are the Trade Union Law, which would restrict labor union strikes; a cybercrime law that could criminalise online communications deemed to undermine the government; and a telecommunications law that would allow the government to monitor online communication and mandate information on its critics from Internet service providers.