Turnbull loses senator's vote on ABCC

A key crossbench senator has withdrawn his support for laws to reinstate the building industry watchdog.

Liberal Democrat David Leyonhjelm was expected to support the bills based on the coalition's support for his sunset clause amendment.

But Senator Leyonhjelm told Sky News on Tuesday the government's plan to change the Senate voting system had forced a change of heart.

"Now they say `Thanks very much - we are going to put you out of business' I am reconsidering my position," he said of the workplace laws.

The senator said he had tended to give a lot of government legislation the benefit of the doubt.

"I don't have to do that anymore," he said.

Senator Leyonhjelm said he expected the government to go to a double-dissolution election in July.