Federal Employment Minister Michaelia Cash has ramped up the attack on opposition to reintroducing the building and construction watchdog, describing Labor senators as a "disgrace" and asking how they can sleep at night when presented with evidence of bullying and thuggery on the nation's construction sites.

The strength of the criticism appears to be further evidence of the Coalition's plans to use the legislation, likely to be blocked by the Senate, as a trigger for a double dissolution election.

The Government had wanted the Senate to begin debate on a bill to reintroduce the Australian Building and Construction Commission (ABCC) earlier this month.

However, Labor and the Greens teamed up with crossbench senators to send the bill to a committee which would not report back until mid-March.

That gives the Government only three sitting days to debate and pass the bill before budget day on May 10.

The deadline for a double dissolution is May 11.

Government senators used Senate Question Time to ask the Employment Minister about examples of bullying and threatening behaviour by union officials, as outlined in the hearings of the Royal Commission into Trade Union Governance and Corruption.

Senator Cash listed evidence of alleged bullying in the ACT, New South Wales, Queensland, SA, WA and Victoria — including CFMEU Victorian state secretary, John Setka.

"John Setka threatens public servants at the ABCC saying, 'Just remember one thing, when this is all over and they don't exist anymore, we will remember them because we know every expletive one of them, we'll never forget them'," Senator Cash said.

"Then a flyer that we heard about at Senate estimates that was circulated on construction sites in Melbourne, this is what it said to the workers: 'To all the dogs out there, remember when you pick up the phone to the ABCC rats, we will know about it and who will protect you when the rats can't even protect themselves?'

"At Senate estimates it's been revealed a female building inspector received a series of unsolicited and unwelcome phone calls from the assistant secretary, Shaun Reardon.

"The inspector also received a call in which an anonymous individual said that he and seven other men were going to come around to her house and gang rape her."

How do you sleep at night?: Cash hits out at Cameron

Earlier Senate president Stephen Parry said he would be referring the use of offensive language used by Senator Cash in describing such evidence to the Senate's procedure committee.

Senator Cash had quoted the language used on work sites, drawing the ire of the Opposition.

"Those on the other side have the audacity to come into this place and stand up and say they do condemn this type of behaviour," Senator Cash said.

"Look in the mirror, look at this type of behaviour. If it was undertaken in any other workplace in Australia, quite frankly, criminal charges would be brought against you in breach of safety legislation.

"But those on the other side, hypocrites as they are, they can only feign outrage at the language used in the Senate."

Senator Cash also took issue with heckling from Opposition benches.

"I will pick up on Senator Cameron's interjection, 'All the Oscars have been awarded'," Senator Cash said.

"Senator Cameron, this is not a show, this is not a game, this is real-life behaviour on construction sites in Australia and you sit there and you give the thumbs up to this type of behaviour.

"Quite frankly you are a disgrace when you stand there and do not condemn this type of behaviour.

"I honestly ask you, how do you sleep at night?"

Coalition frontbencher Christopher Pyne said it would be "very difficult" for the Coalition not to call a double dissolution election if the Senate again rejected legislation to create a construction industry watchdog.

Prime Minister Malcolm Turnbull said the legislation to re-establish the ABCC was "absolutely vital", but he again played down the chances of a double dissolution election in July.

"While all constitutional options remain open, my expectation is and assumption is that the election will be held in the normal way at the normal time which is August, September, October this year," Mr Turnbull said.