More than 1,300 low-wage workers in northern California will get about $6.8 million in back pay from nursing homes and other long-term care facilities as a result of an ongoing U.S. Department of Labor probe uncovering lost wages and minimum wage law violations.

Residential care facilities were a prime target in the now four-year federal probe because many facilities hire immigrants who are ignorant of wage and overtime laws, Assistant District Director Michael Eastwood told a local newspaper. Some of those facilities even allegedly retaliated against workers who questioned their paychecks, according to the Department of Labor. One provider reportedly punished employees who reported violations by placing some of them on unpaid “vacations” for a week, and by making plans to sell the home to new owners who would replace the entire staff.

Nursing homes shouldn’t necessarily be singled out, however. One national survey several years ago found that 26% of low-paid workers across many sectors said they had been paid below minimum wages the previous week, and 76% of those who worked more than 40 hours the previous week said they hadn’t been paid overtime.

In 1997, the department’s Employment Standards Administration’s Wage and Hour Division investigated 288 skilled/intermediate care nursing homes and other personal care facilities to determine the level of compliance with the minimum wage. The biggest proportion of offenses that year involved overtime infractions; only 13% of the facilities paid some low-wage employees below the minimum wage. The current federal minimum wage is $7.25 per hour.