Cambodian police have detained seven workers at a factory that makes clothing for the U.S. sportswear company Nike in the latest strife linked to a strike over salaries there.

Free Trade Union of Workers of the Kingdom of Cambodia organizer Son Vanny said its members traded barrages of sticks and stones Monday with members of a rival union opposing the strike. He said police then arrived and started beating workers. Police declined comment on any arrests or possible injuries.

The protest at the Taiwanese-owned Sabrina (Cambodia) Garment Manufacturing plant west of Phnom Penh began May 21 over demands that salaries be raised to $88 per month from $74. Police used force when the workers blocked main road outside the factory on May 27, allegedly causing two pregnant workers to miscarry.