The New South Wales government is investigating whether the federal government is trying to improperly influence the Fair Work Commission.
It comes as the state gears up for a showdown with the rail union in the tribunal on Tuesday.
Last week, the Federal Minister for Employment and Workplace Relations, Tony Burke, wrote to the Commission stating the government's intention to make legislative changes which would limit an employer's ability to terminate enterprise agreements.
The move angered the NSW government, which had just threatened to tear up the state's rail workers industrial agreement, as part of its bitter dispute with the union and its state secretary Alex Claassens.
The state's Liberal Minister for Employee Relations, Damien Tudehope, labelled Mr Burke's letter a "disgrace" and a "brazen intervention of Labor".
"Tony Burke's 'wink and a nod' letter to the Fair Work Commission President is all about pressuring the Commission to kick the rail dispute as far down the road as possible, so he can legislate to give the unions even more power," Mr Tudehope said.
"This sends a clear message to Alex Claassens and the rail unions: keep up the strikes, Labor has your back."
Mr Tudehope says he is considering taking action.
"I will be seeking advice as to whether Tony Burke's letter constitutes improper influence of the Fair Work Commission under section 674(5) of the Fair Work Act," he said.
In a statement, Mr Burke said his letter to the Commission did not make reference to the rail dispute.
"I made clear last month that in any pay negotiation, it was unreasonable to threaten significant cuts to people's pay by cancelling agreements," he said.
"Those comments were made in the context of a dispute involving the tugboat operators that Dominic Perrottet described as "heroic" and "incredibly impressive".
"I made no reference in that letter to any particular dispute."
The NSW government and the rail union are set to appear before the Commission on Tuesday.
The union applied for the hearing in an attempt to force the government to continue negotiating the rail worker's enterprise agreement.
Last Wednesday, on a day when the rail network was crippled by industrial action, Premier Dominic Perrottet threatened to tear up the industrial agreement unless the union stopped striking and accepted the government's offer.
The Premier gave the union a deadline of Friday to cease all industrial action.
But the government did not follow through on its threat. Instead, it was deferred after the union's legal move.
The government is now waiting for the outcome of the Commission hearing.
While trains are expected to operate as normal this week, there is some ongoing action, including leaving ticket gates open.
