Firms could have to pay millions of pounds to care staff after a woman received £1,250 following legal action over the minimum wage, according to lawyers.
Caroline Barlow, 56, from Devon, claimed she was not paid for the time she spent travelling to and from appointments.
She accepted an out of court settlement from her former employers, MiHomecare.
Jasmine Patel from law firm Leigh Day, which represented the mother of two, said: "Ms Barlow's travel to and from appointments was a necessary part of her job and as such, she should have been paid for it.
"We believe there are potentially thousands more care workers, working for MiHomecare, and other care providers, who are being paid less than the national minimum wage and we would urge them to come forward."
Ms Barlow worked for the company for four months, attending an average of eight appointments a day.
Lawyers believe there could be thousands of similar claims, leading to potential payments of millions of pounds.
MiHomecare has said that since last year, it has been correcting carers' pay where it has been found to be wrong.
Dave Prentis, general secretary of Unison -, which has been campaigning for carers to be paid travelling time, commented: "When someone is working they must be paid for their time. It doesn't matter whether they are driving to the house of the next person they look after or administering care, they are at work.
"But with over complicated payslips, some homecare firms deliberately make it difficult for people to question their wages.
"There must be no hiding place for these minimum wage cheats. At a debate in Westminster next week we'll be backing MPs calling for the Government to step up its efforts to end the scandal of the 200,000 care workers still paid below the minimum wage."