The Australian Industry Group wants an industrial relations freeze until new senators take office.

The major business lobby wants crossbench senators not to pass any industrial relations changes if Parliament sits before the Senate changes over.

The group is worried that, particularly if Labor wins the federal election, the new government may try to hurry industrial relations changes through the existing Senate before senators elected in the May 18 vote take their places.

While members of Parliament are sworn in once results are officially declared, new senators do not commence their terms until July 1.

“There is a need for genuine consultation with industry about all the proposed changes to workplace relations laws before and after any legislation is drafted,” Ai Group chief executive Innes Willox wrote in a 14-page letter to the current crossbench senators.

“Many of the changes that have been proposed by one or both of the major parties would have major adverse impacts on businesses, employees and the broader labour market.”

The Ai Group is worried about Labor’s proposal to wind back Sunday and public holiday penalty rate cuts, which were instituted by a ruling of the Fair Work Commission (FWC).

Mr Willox said Labor's commitment to rolling back the penalty rate cut within 100 days of taking office would require the Fair Work Amendment (Protecting Take-home Pay) Bill 2017 to be moved forward.

This may limit the FWC's ability to make any changes to awards likely to reduce the take-home pay of employees, he said.

“What is the point in having an independent umpire if the umpire is only able to rule in favour of one of the parties?” Mr Willox asked rhetorically.

“The bill makes a mockery of the notion of having an independent tribunal to maintain awards.”