Nicola Sturgeon has been urged to take action to stop workers on public contracts in Scotland having to pay in order to receive wages.
Scottish Labour leader Richard Leonard said his party had evidence that workers on the flagship Aberdeen bypass project are among those affected.
He said one worker for a railway electrification project at Shotts for the now-collapsed outsourcing giant Carillion had to pay £100 to get wages.
Speaking at First Minister's Questions, he said: "Does the First Minister think it is acceptable for workers to be charged up to £100 a week simply to receive their wages?"
He criticised the Scottish Government's action on making work fair and said none of the major outsourcing firms such as G4S, Mitie, Capita and Serco so far have signed up to the voluntary Scottish Business Pledge on fair work practices.
The First Minister said she "condemned any company" making workers pay to receive wages and urged the firms mentioned to sign up the pledge.
She then hit back at Mr Leonard, urging him to come join in with "equipping" Holyrood to come up with solutions as she said that many of the problems were due to employment law being reserved.
Ms Sturgeon said: "The Scottish Labour Party have long opposed employment law being devolved to this parliament.
"So, if the Scottish Labour Party wants to enable this government to take tougher action on practices like that will he join me today, now, in calling for employment law to be devolved to this parliament in order that we can do exactly that?"
Mr Leonard said the issued was public procurement, not employment law.
He said: "Your government is handing over millions of pounds of public money to these companies and they are treating workers shamefully."
Referring to the Aberdeen bypass construction programme, he said: "On a contract funded by your government workers have been blatantly exploited."
Ms Sturgeon said the Scottish Government has gone further than most other governments in the UK in terms of the action on the living wage, zero hours contracts and blacklisting.