Major voting changes have been passed in Queensland, with Parliament approving four more MPs and a return to compulsory preferential voting.

Key points: 'Just vote one' scrapped in surprise laws

'Just vote one' scrapped in surprise laws ALP would have got 8 extra seats in 2015 under compulsory preferential voting

ALP would have got 8 extra seats in 2015 under compulsory preferential voting LNP outraged over lack of consultation

It will now be compulsory to number every square on the ballot box, a move which would have given Labor an extra eight seats and a majority government in last year's election.

In what was a see-saw battle for control of the legislative agenda, Labor managed to force through an amendment to a Liberal National Party (LNP) bill.

The LNP's Electoral (Improving Representation) and Other Legislation Amendment Bill to increase the number of seats from 89 to 93 was set to pass with crossbench support.

But in a surprise move, Attorney-General Yvette D'Ath proposed an amendment to also include the reintroduction of compulsory preferential voting.

Katter's Australian Party and independent MPs supported the bill to number all boxes.

Act of 'corruption and bastardry'

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The LNP accused Labor of being opportunistic and undemocratic by rushing through changes without it going to committee for review.

"This is the most disingenuous act of corruption and bastardry that I've ever witnessed in this Parliament," Ros Bates said.

If the party won the next election, Opposition Leader Lawrence Springborg said they would move to change the system back.

"We would put it to a proper consultative process to the people," Mr Springborg said.

Leader of the House Stirling Hinchliffe defended the lack of consultation, adding that the LNP's bill to add more electorates had no consultation either.

"This change to increase the size of the House to 93 members happened in an unheralded and unprecedented way as a consequence of the Opposition's actions and the majority of the Parliament's actions," he said.

"So we've seen a majority of the Parliament also move to take up compulsory preferential voting."

Changes benefit Labor, analyst says

The ABC's election analyst, Antony Green, said the ALP could have won eight extra seats and been able to form majority government if compulsory preferential voting had been in place at the last state election.

Those seats include Albert, Burdekin, Gaven, Glasshouse, Mansfield, Mt Ommaney, Redlands and Whitsunday.

"What we've seen in recent years is that optional preferential voting has worked against Labor because it gives Green voters another option," Mr Green said.

"They can choose to sit on their hands and not direct preferences.

"And increasingly Labor is more and more reliant on Green preferences."

Mr Green said the Government's argument that reintroducing the compulsory preferential voting would lead to fewer informal votes, was also questionable in light of recent elections.