An upcoming ruling by California's highest court in a legal battle between the union launched by labor leader Cesar Chavez and one of the nation's largest fruit farms could dramatically reduce the power of organized farm labor in the state.

The California Supreme Court was expected to decide Monday whether a law allowing the state to order unions and farming companies to reach binding contracts is unconstitutional.

Labor activists say the mandatory mediation and conciliation law is key to helping farm workers improve labor conditions.

Opponents say it's government overreach that deprives agricultural employers and workers of a say over wages and other terms of employment.

The state Supreme Court's ruling will come in a lawsuit pitting Gerawan Farming, which hires thousands of workers for its nectarine, peach and plum farms, against the United Farm Workers of America.

The 2002 state law at issue allows the California Agricultural Labor Relations Board to order mediation to achieve a labor contract for farm workers and gives mediators the authority to set the terms of the agreement.

Unions can seek mediation 90 days after demanding to bargain on behalf of workers — even if the vote to unionize occurred decades earlier in some cases.

"The argument when it was enacted was that workers would get all fired up about having a union to represent them and they would vote for the union but then the employer would delay and the workers would lose their enthusiasm," said Philip Martin, a farm labor expert at the University of California, Davis.

In court documents filed with the state Supreme Court, the UFW says a previous law had failed to achieve the state's goal of providing millions of farm workers with the right to bargain collectively with employers.

As of 2002, less than half of farm employers whose workers voted to join a union since 1975 had agreed to a labor contract, according to the UFW.