The federal government has not done any modelling on the impact of the Fair Work Commission's decision to cut penalty rates, responses to a Senate hearing have revealed, despite Prime Minister Malcolm Turnbull throwing his weight behind the cuts.

In answers to questions on notice from Senate estimates to be released on Friday, Treasury said it would assess a range of policy decisions when reviewing forecasts for the upcoming May budget.

"But this would not entail a specific modelling of the Fair Work Commission recommendation," a statement from its macroeconomic division said.

"There are likely to be some positive employment effects from a reduction in penalty rates, though it is difficult to quantify the precise effect."