PHNOM PENH, Cambodia (AP) — Cambodian police on Monday clashed with workers and arrested seven at a factory that makes clothing for the U.S. sportswear company Nike in the latest violence linked to a strike over salaries there, a union organizer said.

Free Trade Union of Workers of the Kingdom of Cambodia organizer Son Vanny said its members exchanged barrages of sticks and stones with members of a rival union opposing the strike, after which riot police arrived and started beating workers. He said seven workers were arrested, but police at the scene and at the Interior Ministry declined to comment on any arrests or possible injuries.

The protest at the Taiwanese-owned Sabrina (Cambodia) Garment Manufacturing plant in Kompong Speu, just west of the capital, Phnom Penh, began May 21 when workers demanded that their salaries be raised to the equivalent of $88 per month from $74. Their net pay is calculated to include overtime and various allowances.

Police allegedly used force when the workers blocked the main road outside the factory on May 27, reportedly causing two pregnant workers to miscarry. Nike, for whom the factory is a subcontractor, expressed concern about the situation.

After Monday's incident, Son Vanny accused police of beating and detaining only workers from his union. He said police alleged the workers had incited violence, a charge he denied.

Heng Sophors, an activist with the local human rights group Licadho who monitored the event, said that more than 1,000 riot police with batons and shields were deployed around the factory, and that some were also the targets of sticks and stones thrown by the protesters. He said some strikers were slightly injured when police waded in to try to restore order.

The garment industry is Cambodia's biggest export earner, employing about 500,000 people in more than 500 garment and shoe factories. In 2012, the Southeast Asian country shipped more $4 billion worth of products to the United States and Europe.

Pay is low and working conditions are usually uncomfortable at best. Last month, the ceiling of a Cambodian footwear factory collapsed, killing two people and injuring seven.

However, Cambodia hosts a unique program of the International Labor Organization called "Better Factories Cambodia" that assesses and reports on working conditions in all the country's export garment factories. The impetus for the program was an agreement under which Cambodia pledged better labor conditions in exchange for better trade privileges with the United States.

Because the industry is Cambodia's economic locomotive, garment workers also carry some political clout, a special concern for Prime Minister Hun Sen's government because it is an election year and some unions have long-standing ties with the political opposition.