Union leader Bob Crow has clashed with Transport Minister Tavish Scott over the 48-hour rail strike.
Bob Crow said Acas decisions cannot be enforced
On BBC Scotland's Good Morning Scotland programme, the RMT general secretary reacted angrily to comments that the union should have gone to Acas.
Speaking on the programme later, the minister said the arbitration service should have been used in a bid to settle the dispute.
Mr Scott also said the threat of a UK strike was a "throwback to the 70s".
Signal staff are striking over how the implementation of a new 35-hour week.
An agreement has been reached in other parts of the UK.
Mr Crow told the programme: "The reality is that we reached an agreement with the company, but management reneged on that.
"Acas can't force the union or the company to accept a decision it makes."
He said that if the dispute was not settled by next Thursday all signal workers in the UK would be balloted.
Speaking on the radio programme, Mr Scott said: "I thought we were getting an interview there thrown back from the 1970s rather than 2007.
"The arbitration service is designed to sort out these kind of problems but they (the union) don't want to use that.
"The problem here is for rail passengers and it's extremely unfortunate and should not be happening."
Mr Scott added that it was not up to the Scottish Executive to resolve the issue as it was not the employer.