The union representing workers at Ralphs, Vons and Albertsons grocery stores has approved a strike as negotiations with the grocery chains have soured.

The move gives the United Food and Commercial Workers the option to strike if there’s an impasse and provides the union with a powerful bargaining chip. A 2003 strike by the union deeply hurt the supermarket operators by cutting into their market share.

Grocery union employees have been working with their employers to renegotiate a 3-year-old contract that expired in March.

In April, a federal mediator was called in to help speed up negotiations, but progress has been slow as the two parties remain far apart on wages and health care.

Union officials claim the grocery stores want to cut wages for cashiers by downgrading their job tiers while other workers would see less than a 1% pay raise. They also argue that a reduction in cash dedicated to a group health care plan could tilt the fund toward bankruptcy.

John Votava, a spokesman for Ralphs Grocery Co. Inc., which is held by Ohio-based Kroger Co., said the authorization to strike doesn’t mean one will occur.

“We have a contingency plan in place to ensure our stores remain open to provide fresh, in-stock merchandise for our customers,” he said in an email.

The next round of negotiations is slated for July 10.

Manufacturing, retail and trade reporter Rachel Uranga can be reached at [email protected] or (323) 556-8351. Follow her on Twitter @racheluranga.