(Adds details, context, some mines where unions will be striking)
LIMA, May 15 (Reuters) - Workers at several major mines in Peru, including two of the country's top copper producers, plan to go on an indefinite strike on Monday in a country-wide bid to press the government to strengthen labor laws, union bosses said.
The planned work stoppages at more than 20 mines threaten to curb mineral production in Peru, the world's third-biggest copper, silver and tin producer and seventh-biggest gold producer.
Unionized workers are demanding the government repeal a law passed last year that eases rules on firing workers and to restrict the use of contract workers by mining companies, said Ricardo Juarez, the president of a national mining federation.
The strike also aims to shelve legislation that mining unions say reduces benefits and workplace inspections.
"We're not asking for a wage increase," Juarez said. "We want a series of norms and decrees that go against mining workers eliminated."
Some 20,000 workers are part of the national mining federation, Juarez said.
The labor ministry declared the planned stoppage unfounded, an action that allows for an appeal process and often does not stop unions from striking.
However, the president of Peru's mining chamber said he did not think the strike would significantly affect the country's mining production. "They have planned this for years and set dates, but in many cases it is suspended," said Carlos Galvez.
The following are some of the mines where Juarez said unionized workers will take part in the strike. Production levels are from the energy and mines ministry.
-ANTAMINA Produced 362,000 tonnes of copper and 266,000 tonnes of zinc last year. BHP Billiton Ltd and Glencore Plc own 33.75 percent stakes. Teck Resources Ltd controls 22.5 percent and Mitsubishi Corp 10 percent.
-CERRO VERDE Produced 235,000 tonnes of copper last year. Freeport-McMoRan Inc controls 53.56 percent, Sumitomo Metal Mining Co Ltd 21 percent, Buenaventura 19.58 percent.
-ANTAPACCAY The Glencore-owned mine produced 167,000 tonnes of copper last year.
-SHOUGANG Produced 7.2 million tonnes of iron last year. Owned by China's Beijing Shougang Co Ltd.
-SAN RAFAEL Local miner Minsur SA produced 23,100 tonnes of tin from the deposit last year.
Reporting by Lima Newsroom; Editing by Ken Wills and Lisa Shumaker