Money owed to 291 workers in Corby has been paid and two employment agencies have been told to pay penalty charges.
National minimum wage officers and Employment Agency Standards staff visited 34 employment agencies in Corby between May 28 and May 30.
Twelve agencies were identified where workers were potentially being underpaid.
Two of the 12 investigations have now been completed and wage arrears totalling £3,154 have been paid to 291 workers.
The two agencies involved have received automatic penalty charges totalling £1,532.
Investigation of a further five employment agencies in the town are continuing and it has been revealed that a further £120,000 in wage arrears could be owed to more than 3,500 workers.
That would mean the employers involved would face a total of £15,000 in penalty charges.
MP David Gauke, the Minister responsible for HMRC, confirmed the latest position on investigations but said he was bound by a duty of confidentiality not make any comment on ongoing, planned or anticipated legal proceedings.
Corby MP Andy Sawford who worked with Her Majesty’s Revenue and Customs (HMRC) on the investigation, said: “I am determined to stop employment agencies from exploiting local workers.
“After meetings with the Employment Agency Standards Inspectorate and with the government Minister responsible, I was pleased to welcome a major joint task force to Corby.
“As I feared, they found very significant issues of exploitation and I have been working to make sure that these lead to action.
“Two agencies have already paid the price for flouting the law and 10 more are under investigation.
“I am delighted that local workers have been getting money back that was owed to them but the amounts returned so far are the tip of the iceberg and I will be keeping the pressure up to make sure that all the investigations are followed through.
“Frankly, I think these employment agencies should be named and shamed for ripping off local workers, rather than being able to hide behind confidentiality.”