Australia appears to be on a path for a July 2 double dissolution election, as the Senate again rejected the Government's bill to re-establish the construction watchdog.

The Government lost the vote 36-34.

Senators Bob Day, Dio Wang, David Leyonhjelm and Nick Xenophon all voted to give the bill a second reading.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 6 minutes 31 seconds 6 m George Brandis says constitutional grounds for a double-dissolution election exist

But the Opposition, Greens and the remaining crossbenchers — Jacqui Lambie, Ricky Muir, Glenn Lazarus and John Madigan — all voted the bill down.

MPs and senators were recalled to Canberra three weeks early for an extraordinary sitting of Parliament to debate two pieces of industrial relations legislation.

The first of those bills, which seeks to bring back the Australian Building and Construction Commission, was reintroduced this morning.

It had already been voted down by the Senate once before and on Monday afternoon it was blocked again.

Last month, when announcing he had asked Governor-General Sir Peter Cosgrove to prorogue Parliament for the extraordinary sitting, Prime Minister Malcolm Turnbull said Australia would head to a double dissolution election on July 2 if the bill was blocked.

It will be a long and hard campaign: Labor

The second part of the Government's suite of industrial relations legislation, the Registered Organisations bill, has already been blocked twice.

It is almost certain the Prime Minister would call the election after the federal budget is delivered on May 3.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 5 minutes 33 seconds 5 m Penny Wong says she does not think the Prime Minister has got a plan for the Government

Mr Turnbull must call a double dissolution election before May 12, otherwise it can only be a standard poll to elect the House of Representatives and half of the Senate.

Parliament continued sitting on Monday night until it had also dealt with legislation to abolish the Road Safety Remuneration Tribunal.

That bill passed the Senate just before 10pm.

Attorney-General George Brandis told the ABC that "constitutional grounds for a double dissolution election exist".

But Senator Brandis said tonight's actions did not equate to the start of an election campaign.

"It is not really an election campaign until the Parliament is dissolved and the writs are issued, in my view," he said.

Opposition Senate leader Penny Wong said Labor was ready for an election campaign.

"It will be a long campaign and a hard campaign," she said.