Editor’s Note: The third graph of this story has been changed to correct a description of the nature of the benefit funds in project labor agreements.

In a victory for nonunion contractors, the Palmdale Water District has become the first government body in Los Angeles County to ban union-friendly project labor agreements.

The water board on Wednesday voted 3-2 to amend its rules and regulations to prohibit the requirement of project labor agreements, despite heavy pressure from local construction union trades.

Project labor agreements require all contractors on a public works project to hire workers through union hiring halls; in exchange, unions pledge not to stage any work slowdowns or strikes. Many nonunion contractors oppose these agreements, in part because they require them to pay into special funds jointly administered by union and contractor officials.

The Palmdale Water Board is the seventh government body in the state to adopt a ban on project labor agreements. Earlier this year, voters in Oceanside and Chula Vista approved bans on PLAs in those cities.

Next week, voters will decide whether to impose a ban on PLAs in unincorporated San Diego County. Nonunion contractors are also considering placing PLA bans on the ballot in one or more L.A. County cities as early as 2012.