An estimated 7,000 grocery workers at Raley's and Nob Hill Foods grocery stores in Northern and Central California were walking the picket line Monday after 15 months of contract negotiations ended in acrimony.

The strike follows the implementation by Raley's of its "last, best and final" contract proposals, according to the United Food and Commercial Workers 8-Golden State and Local 5. The union accused Raley's of bargaining "in bad faith."

The union also filed unfair labor practices complaints on Thursday, including allegations that Raley's managers have been interrogating and intimidating union members, union officials said.

"We look forward to returning to the bargaining table when Raley's management has adopted a more constructive attitude," a statement from UCFW Presidents Jacques Loveall and Ron Lind said today. "Our goal from the beginning is to negotiate a fair agreement serving the needs of both Raley's and its union employees."

Raley's officials rejected the allegations.

"We're very frustrated that it's come to this, this has been going on for 15 months," said spokesperson John Segale. "We submitted our last and final offer four weeks ago and we never heard from the union, they never let their employees vote on that."

"So we had no choice but to implement our wage package this morning," Segale said.

Segale said Raley's urgently needs to cut costs in a "fiercely competitive" market. He said the Sacramento-based chain, which includes Raley's, Nob Hill Foods and Bel Air stores, has closed five stores in the past year and seen the opening or expansion of 240 non-union stores in its markets since 2008.

The conditions imposed today apply only to wages, Segale said. The store moved to freeze pay increases for two years and eliminate the premiums paid for employees working Sundays, night and holidays, but retained the one week of paid vacation and four paid holidays employees currently receive, he said.

Workers will be picketing stores and asking shoppers to take their business to competing grocery stores, union officials said.

Raley's and Nob Hill Foods have more than two dozen stores located in the Bay Area and more in Monterey and Santa Cruz counties.