The rights organization said it wasn't certain about the fate of a number of labor and trade union activists rounded up by Iranian authorities. All of those arrested were members of unions not sanctioned by Iranian law.
"This latest round of arrests continues a long and ugly tradition of targeting independent trade unions to enforce full state control over these groups," Stork said.
Human Rights Watch said most of the arrests followed demonstrations demanding back wages. The president of a bus workers' union, the rights organization said, was given a five-year prison sentence for making "propaganda against the state."
The organization had expressed concern about the recent crackdown on reformist newspapers in Iran. Human Rights Watch said it was worried that Iranian authorities were trying to silence their critics ahead of parliamentary elections scheduled in March.
"Labor activists have been at the forefront of the struggle for freedom of association and assembly in Iran and they have paid a heavy price," added Stork.
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