The fastest-growing U.S. job is home health aide, yet many are paid under the federal minimum wage of $7.25 an hour, the Domestic Workers Alliance says. A study released by the National Domestic Workers Alliance -- a group of nannies, housekeepers and caregivers for the elderly -- found nearly a quarter of home health aides earn below minimum wage, CNNMoney reported. The U.S. Congress decided in 1974 to classify home health aides together with casual babysitters under labor laws allowing employers to pay less than the federal minimum wage and to not pay overtime. Companionship workers, by definition, spend at least 80 percent of their workweek keeping a patient company or playing cards with him or her, but once they spend more than 20 percent of their time cleaning or cooking they should qualify for minimum wage and overtime. The large agencies said they keep careful records to determine when workers cross over the 20-percent line. The agencies also said they should not pay time-and-a-half to workers who often stay overnight with their patients because an home health aide might do little more than help a patient walk to the bathroom once or twice. However, often the elderly are wide awake in the middle of the night and have trouble going back to sleep, want something to eat or need to change clothes after an accident. A caregiver could be up half the night. Home care agencies said if forced to raise wages and pay overtime, they\'ll have to restrict workers to 40 hours a week to keep costs down and seniors might turn to undocumented workers. Home care workers are already entitled to state minimum wages in 21 states and at least 15 states require overtime pay for those who work more than 40 hours a week, CNNMoney said.