A group representing some of the largest apparel brands in the US and Europe – including Gap, H&M and ASOS – expressed “growing concern” on Tuesday over several controversial labour laws and ongoing court cases against unionists described as restrictive and unjust.

In an open letter to Prime Minister Hun Sen, the apparel groups also call for amendments to the contentious 2016 Trade Union Law and ask the government to strengthen the Arbitration Council, a dispute resolution body that has gained a reputation for fairness and independence.

Since the passage of the Union Law, the number of cases heard by the council has plummeted, which unions attribute to the law’s onerous registration rules and other restrictions on unions’ activities.

In the letter, the group, which includes the US-based trade group American Apparel & Footwear Association and the UK-based advocacy group Ethical Trading Initiative, warns that restrictions on freedom of association “will make Cambodia an unattractive and expensive place to do business”.

The groups also call for an end to the harassment of labour activists like Central Director Moeun Tola and Coalition of Cambodian Apparel Workers’ Democratic Union President Ath Thorn, both of whom are facing criminal charges.

“Five months have passed with little progress in your government fulfilling those commitments,” the letter reads.

In addition, the organizations also ask the government to drop a proposed ban on independent research during the minimum wage negotiation process, as well as a controversial draft law on labour disputes – two floated measures that the Ministry of Labour had already said it would scuttle in October 2017.

The group has asked for a meeting with the premier to discuss its concerns.

Heng Sour, the spokesman for the Ministry of Labour, said “most of the language” in the letter was out-of-date and “not representing reality”.

In particular, he said, the ministry already withdrew the proposed research ban, as well as the labour dispute draft law.

“The ministry will update the facts and real information to the concerned parties once we officially receive the letter,” Sour said.

Asked why the apparel groups had not been informed of the changes, Sour blamed people with “bad intentions” for misleading them. “Our friends will be happy with what we update them on. They might stop sourcing their information from ill-minded informants in the future,” he said.

Cambodia’s garment industry, which employs more than 700,000 people, is a backbone of the country’s economy, and government officials have expressed concern about potential sanctions from the US and European Union stemming from an ongoing crackdown on the political opposition, civil society and dissenting voices.

Lawmakers for the now-defunct Cambodia National Rescue Party – whose leader was jailed and whose forced dissolution prompted an international outcry – have lobbied international brands and buyers to put pressure on the government.

Former CNRP lawmaker Mu Sochua said the ousted lawmakers have been in touch with the groups in the letter, which she said “demonstrates the brands’ serious concern of the political situation”.

“Ignoring their call for specific actions can lead to their pulling out,” Sochua said in a message. “Not good for the industry when the EU and US considering economic sanctions.”

Ken Loo, of the employer-representing body Garment Manufacturers Association in Cambodia, declined to comment in detail on the letter, but questioned how the Union Law had hindered unions’ rights.

But Solidarity Center Senior Program Officer Khun Tharo said he shared the concerns listed in the letter, including lack of progress on addressing recommendations shared by the International Labour Organization in July.

“So far, we don’t see any action yet in terms of government action to implement that road map,” Tharo said.

“I would believe that the government would consider and would take some significant steps to improve and address the concerns” in light of the letter, he added.