SAN FRANCISCO (AP) — Wal-Mart could be on the hook for more than $100 million in back pay after a federal judge ruled the company failed to pay California minimum wage to truck drivers for activities that included inspecting and washing their trucks, an attorney said Wednesday.

The ruling came after the company argued that the drivers are paid for particular activities that include those tasks.

U.S. District Judge Susan Illston sided with the drivers in her May 28 ruling, saying activities that are not compensated separately cannot be included in tasks that are paid for by the company.

“These guys are owed the money, so the sooner they get paid, the better,” said Butch Wagner, whose firm represents 720 past and current Wal-Mart drivers.

Wal-Mart spokesman Randy Hargrove said the Arkansas-based company will keep fighting the wage claim. Its drivers are among the best paid in the industry, with some making more than $100,000 a year, he said.

Wal-Mart Stores Inc. — the nation’s largest private employer — has faced other criticism over its pay and treatment of U.S. employees.

The company announced earlier this year that it was giving a raise to about a half-million U.S. workers. The raises are part of a $1 billion investment the company says is also intended to give workers more opportunities to advance and more consistent schedules.

In court filings, Wal-Mart attorneys likened the drivers’ situation to housekeepers getting paid for each house they clean rather than by the hour.

“Nothing in the Labor Code requires a separate ‘pay code’ for each act that goes into cleaning the house,” the attorneys said in court papers. “Does the Labor Code require drivers to be separately paid for putting a key in the ignition or while sitting at a stop light?”

The drivers said Wal-Mart did not pay them properly for layovers and did not pay them at all for tasks such as weighing their tractor-trailers and completing mandatory paperwork.

Wal-Mart drivers are not paid by the hour. Wages are based on mileage and specified activities.

Illston sided with the drivers on the layover issue as well.

The case is set to go before a jury in April to determine damages, Wagner said. He estimated Wal-Mart could face penalties, damages and interest of as much as $150 million.