Labor expects a swing against the party at an upcoming by-election, as tax cut changes failed to give a larger boost in polling.

Voters will head to the ballot box in the Victorian seat of Dunkley on Saturday, following the death last year of Labor MP Peta Murphy.

The Resolve Political Monitor, published in Nine newspapers, and the Newspoll, published in The Australian, show Labor has lost some edge on the primary vote.

The latest polling reveals Resolve has the coalition at 37 per cent against Labor at 34 per cent, while Newspoll shows the coalition ahead at 36 per cent compared to Labor at 33 per cent.

Cabinet Minister Murray Watt said by-elections were always tough for incumbent governments.

“It would be reasonable to expect to swing against the government … if we can manage to have a win, and hold on to that seat, then we’ll be very happy,” he told ABC News on Monday.

Resolve asked about 1600 voters if they supported Labor’s changes to the stage  three tax cuts, which increased tax breaks for lower paid workers while lowering the benefit for higher income earners.

More than half – 52 per cent – backed the change while 14 per cent opposed it, with 35 per cent undecided.

A breakdown of income categories showed all voters backed the change, including those earning more.

Asked if they viewed Labor’s changes as a broken promise, given the party went to the last federal election promising no change, 46 per cent said that changing the policy to “suit the times” was sensible.

Another 34 per cent said it amounted to a broken promise.

But 61 per cent said it didn’t make them think differently about the prime minister.

Newspoll surveyed 1245 voters between February 19-23.

Environment Minister Tanya Plibersek said her party held the seat on a six per cent margin, when governments on average recorded an eight per cent swing against it in by-elections.

“We always knew that the Dunkley by-election would be very close,” she told Seven’s Sunrise.

Former prime minister John Howard joined the opposition’s bid to win the seat, urging voters to send Labor a “wake-up call”.

In a message, Mr Howard said the government had done a poor job of tackling inflation which was impacting so many Australians.

“It appears increasingly out of its depth in managing the economy and important matters of security,” he wrote.

“In short, Labor needs a wake-up call.”

Nathan Conroy, the mayor of Frankston City Council, is contesting the seat for the Liberal Party.

Nationals MP Barnaby Joyce said Mr Conroy had a “big job” to win the seat, but voters had a reason to vote against the government. 

Frankston community leader Jodie Belyea will aim to retain the seat for Labor’.

Opposition finance spokeswoman Jane Hume said the mood in the electorate was one of anger towards the government over cost of living pressures, but conceded it was going to be a tough contest.

“There is no doubt about it,” she told Sky News.

Independent MP Helen Haines introduced a private members’ bill on Monday in the House that would require government grants to follow a merit-based selection process to bolster integrity measures.

Dr Haines said rorting wasted money and destroyed public trust in government, as she called for the rules to be strengthened before the next federal election.

This post was originally published on Michael West.