Long day and night ahead for senators

By Belinda Merhab and Elise Scott

At least one angry crossbencher has vowed to make the Senate sit through the night and possibly longer as it debates changes to the way Australians elect senators.

Parliament's upper house is debating government legislation that threatens to prevent micro-parties from winning Senate seats.

Family First senator Bob Day said the crossbench owes it to the three million Australians who didn't vote for one of the three major parties to fight back, telling reporters in Canberra: "We'll do that right through the night if we have to".

Labor senator Sam Dastyari said the opposition, which opposes changes, isn't going anywhere.

"Bring your pillows, bring your mattresses," he said.

His colleague Doug Cameron expects a long debate on a lengthy list of amendments.

"Stick around, enjoy it," he said.

But Liberal Democrat senator David Leyonhjelm expects the people "who call the shots" to get tired about midnight and decide to come back on Friday.

"The agenda is huge what they want to get through," he said.

The government estimates the legislation will come to a vote around 3am on Friday.

Lower house MPs are on standby to approve amendments adopted by the Senate.