The firms had to pay almost £100,000 to 197 telesales staff after an employment tribunal ruled they were entitled to a higher rate of national minimum wage.
Axis Telecom Ltd, of Shirethorn House, Prospect Street, Hull, was ordered to repay £21,224 in arrears to 14 workers comprising its total workforce, and Servizon Ltd was ordered to repay arrears of £75,117 to 183 of its 201 employees.
HM Revenue and Customs began an investigation after complaint by an employee to its hotline.
HMRC successfully argued at the tribunal, held in Hull, that the workers were not employed under contracts of apprenticeship and were entitled to the higher rate.
A penalty of £5,000 per company was also imposed.
Michelle Wyer, assistant director of national minimum wage at HMRC, said: “We are pleased the employment tribunal has given this ruling in support of the workers who were being underpaid. Our aim is to enforce the law and protect vulnerable workers.”
Servizon ceased trading in November 2010 when it was acquired by Axis Telecom.
Ms Wyer said employers were welcome to approach HMRC at any time for advice through its pay and work rights helpline on 0800 917 2368.