Senate crossbencher Jacqui Lambie has revealed she cooked embattled union boss John Setka a roast lamb to try to convince him to quit.

Senator Lambie invited the controversial union boss to a Sunday roast at her Tasmanian home, before pleading with him for four hours to resign.

She followed it up with another four-hour conversation weeks later and believes he’s close to standing down.

“I’ve got him to the point where he’ll consider it, so how about he goes one step further and actually carries out the action?” Senator Lambie told 3AW Radio on Monday.

A cream cake from the senator’s local bakery was also on the menu.

“I sweetened him up and all, mate. I still haven’t got him over the line yet.”

Mr Setka is under mounting pressure to resign, as the Senate prepares to scrutinise draft laws to deregister rogue unions.

Senator Lambie, who holds a crucial swing vote, has declared she will eventually support the union-busting bill unless Mr Setka stands down.

“I’m going to stay very solid on this – John Setka needs to resign,” Senator Lambie told the Nine newspapers on Monday.

“Either he resigns now or these rules will come into place and he won’t be able to stay on the line and he’s going to go down anyway. Is it worth taking 1.4 million union members down with him?”

However, Senator Lambie said she would try to kill the bill in the coming fortnight of parliament if Mr Setka quit.

“Instead of being such a bloody meathead, he needs to wake up to himself and he needs to resign because he’s doing a hell of a lot of damage,” she said.

The Coalition government has made Mr Setka, who leads Victoria’s construction union, the public face of its union-busting Ensuring Integrity Bill.

He was convicted of harassing his wife – with dozens of vile text messages – in June, and also accused of making disparaging remarks about anti-domestic violence campaigner Rosie Batty. Mr Setka pleaded guilty to the harassment charges but has consistently denied the claims about Ms Batty.

Opposition Leader Anthony Albanese is determined to expel Mr Setka from the Labor Party. However, the embattled CFMMEU leader has refused to go, even taking the battle to court.

The Coalition’s proposed legislation would also make it easier to ban union officials who repeatedly break the law and impose restraints on mergers.

It will be scrutinised by a Senate committee later this week, after passing the lower house in July.

“If he wants to resign and put his members’ interests’ first, then we can probably vote this away and get rid of this bill in the next fortnight,” Senator Lambie said.

John Setka needs to smarten up, says Jacqui Lambie. Photo: AAP

“If I was him I’d bloody smarten up for once in his goddamned life and stand down immediately.”

Deputy opposition leader Richard Marles said the union-busting bill was yet another distraction from the flagging economy and an attempt to wedge Labor.

“This is legislation which is trying to make the work of trade unions more difficult,” he told the ABC.

“When you are thinking about a sluggish economy where wage growth is at the lowest on record, why you would be focused on this beggars belief.”

Labor and the Greens oppose the legislation, so the government needs support from four of the six crossbench senators.

The government is confident of securing support from independent Cory Bernardi and the two One Nation senators, meaning Senator Lambie’s vote would make it law.

Centre Alliance, which controls two votes, supports the measures in principle but believes what goes for union officials should also apply to corporate leaders, directors and chief executives.

-with AAP