Union leaders say they are meeting increasing difficulty opening branches in new workplaces, making it difficult to ensure workers are treated fairly.
"It's discriminating," said Pat Sambo, president of the Cambodian Tourism and Service Workers Federation.
"When we set up unions, they fire workers," he said, speaking as a guest on "Hello VOA" Monday.
The unions should be able to promote cooperation between managers and workers, but that has not been the case, he said.
Workers in recent months have violently clashed with police, in a union climate that has always been volatile.
Pat Sambo's union represents 3,600 workers in sectors undergoing tremendous growth in Cambodia's developing economy.
Unions are meant to protect the rights of workers, Pat Sambo said, encouraging workers who have not joined a union to do so.