Walmart’s policy of paying its truck drivers by miles driven and activities performed violates California’s minimum wage law, a federal judge has ruled, putting the retailer on the hook for as much as $100 million in back wages.

“The court finds that the pay policies detailed in the [company’s trucker] manuals violate California minimum wage law by failing to pay drivers at least minimum wage for all the time they work,” wrote U.S. District Judge Susan Illston.

In 2008 Walmart truckers sued the company, claiming that they were not adequately paid for non-driving tasks such as inspections, rest breaks, fueling, waiting at scales and taking mandatory “layover” periods to reduce fatigue.

Walmart did not immediately announce if it would appeal the ruling.

If you own or operate a small to medium-sized business, managing all your employees plus meeting federal labor laws and regulations can be daunting, especially with new rules being issued all the time. To help you understand your rights and responsibilities in every facet of running a business, please order a copy of Personnel Concepts’ All-On-One HR Compliance Program for Small Businesses.