The United Food and Commercial Workers Union, which represents the Southern California grocery workers who are currently on strike, has said it has filed a US$600m lawsuit against Albertsons and Kroger's Ralphs.

The lawsuit alleges that the two US grocery retail chains violated state law by locking out around 49,000 workers this week.

Contract talks between Safeway's Vons chain and the union broke down last weekend leading to a vote to strike. Albertson's and Kroger's Ralphs then locked out workers under a joint negotiation agreement.

A spokeswoman for Albertsons said the lawsuit was without merit, reported Reuters.