Forces cleared the site of a political opposition camp in Phnom Penh this week. European Pressphoto Agency
A coalition of international retailers condemned Cambodia's violent crackdown on strikinggarment industry workers, while labor advocates criticized the response to the deadly wage dispute as weak.
In an open letter to the Cambodian government, factories and unions, seven major retailers including H&M Hennes & Mauritz HM-B.SK -1.28% AB, Gap Inc., GPS +0.74%Adidas AG ADS.XE -0.11% and Zara's parent company, Inditex SA, ITX.MC +0.97% said they had "observed both the widespread civil unrest and the government's use of deadly force" with "great concern."
Police opened fire Friday on a crowd rallying for higher wages, killing at least four people and injuring dozens.
The crackdown effectively quelled what had been a nationwide strike launched Dec. 24 in Cambodia's largest formal-sector employer and export industry.
In the letter, reviewed by The Wall Street Journal, the brands called on all parties to reject violence and "support the development of a regularly scheduled wage review mechanism, which is fundamental to peaceful wage negotiations in the future."
Labor advocates said that heavyweight retailers should have done more. "There are a number of brands missing from the endorsement. Are they going to speak up or not?" said David Welsh, Cambodia program director for the Solidarity Center, a nongovernmental organization affiliated with the U.S.-based AFL-CIO labor group.
Mr. Welsh said that brands that did sign should have emphasized the importance of protecting unions and labor laws. He said the letter failed to address that at least 23 workers and labor activists have been detained in an unknown location since the protests began.
H&M, Gap, Inditex and Adidas declined to comment on the specific issues raised by the labor advocates.
Union leaders are now in hiding for their safety, said Pav Sina, president of the Collective Union of Movement of Workers. "We want the famous buyers and brands to talk to the Cambodian government to guarantee the safety and protect the rights of unions."
A day after the shooting, police broke up the main rally site of an opposition party that had supported the workers and had been demonstrating against the victory of Prime Minister Hun Sen's ruling party. With the labor and political protests damped, most garment factories resumed production Monday.
Government officials have said security forces acted to protect public interests and workers' safety.

The escalating violence came after garment workers defied government orders to end the strike by Thursday last week, reiterating demands for the industry's minimum wage to be raised to $160 a month—$60 higher than the government's latest offer. An alliance of unions and labor activists estimates that a living wage for garment workers would be $283 a month.
"It's bad that there were deaths and injuries,'' said Van Sou Ieng, chairman of Cambodia's Garment Manufacturers Association. "But when there's violence and force is used, there's always going to be collateral damage. It's difficult to avoid."
Mr. Van said he estimates that the strike cost Cambodia's garment industry roughly $200 million in lost revenue, and that orders may decline 20%-30% in 2014.
The garment sector supplies apparel to retailers mainly in the U.S. and European Union. It earned nearly $5.1 billion in the first 11 months of 2013, up 22% from the same period in 2012, according to the Commerce Ministry.
"Everybody's just waiting for the other shoe to drop. Force is not a long-term solution," said Jill Tucker, chief technical adviser of the U.N. factory-monitoring program Better Factories Cambodia.
Ms. Tucker's organization has waged a bruising battle to improve standards. In September, Better Factories said it would start publicizing the names of factories with safety and other violations rather than keeping them confidential.
Cambodia's factory association said that it wasn't against such disclosures. But it advised plants to make sure Better Factories inspectors be accompanied by government officials or have written permission from authorities.
International brands that backed the Better Factories initiative protested. In an Oct. 15 letter to the association reviewed by the Journal, 13 major international brands including H&M, Gap, Nike, and the Walt Disney DIS +0.69% Company requested that the association "make no further effort to undermine BFC's operations."
Labor advocates said that Tuesday's letter received only about half as much support and questioned why brands such as Nike and Disney didn't sign on this time. Neither brand immediately responded to requests to comment.
Before Tuesday's letter, Nike spokesman Greg Rossiter said that the company was "concerned" about recent incidents and that "the correct approach is for brands to support a process that establishes the proper mechanisms'' for negotiations.
—Sun Narin in Phnom Penh contributed to this article.