CANBERRA, AAP – Big business is urging the government to forge ahead with controversial workplace law reform despite a minister’s leave hampering crossbench negotiations.

Industrial Relations Minister Christian Porter will not be in parliament this week, which is the final Senate sitting until the May budget.

One Nation leader Pauline Hanson and party colleague Malcolm Roberts are meeting with Mr Porter’s temporary replacement Senator Michaelia Cash on Monday.

But the other three minor party and independent senators have signalled they are unlikely to negotiate the legislation without Mr Porter.

The government needs three of the five crossbench senators to back the industrial relations omnibus bill, which is listed for debate in the upper house on Tuesday.

A powerful coalition of employers has urged the coalition government to pass the bill this week, arguing there is no valid reason for the delay.

The joint statement is signed by the heads of the Australian Chamber of Commerce and Industry, Australian Industry Group, Australian Mines and Metals Association and the Business Council of Australia.

The Australian Retailers Association, Master Builders Association, Restaurant & Catering Industry Association, the Nationals Farmers’ Federation are also represented.

“A failure to vote on the bill will increase uncertainty and stifle business confidence at the worst possible time – just before the JobKeeper scheme ends and as businesses are making critically important decisions on whether to retain staff,” the group says.

Crossbench trio Rex Patrick, Stirling Griff and Jacqui Lambie have raised concerns with parts of the bill relating to casual employment.

Government Senate leader Simon Birmingham said negotiations with the crossbench would look at any issues senators raised.

But he said the talks wouldn’t be necessary if Labor supported the legislation.

“This is a bill that increases penalties in relation to wage theft, it’s a bill that deals with sham contracting,” Senator Birmingham said.

“It’s a bill that provides greater certainty in relation to casual employment and greater opportunity in relation to part-time employment.”

After this week, the Senate will sit for just three days in budget week, before returning in mid-June.