Bill Shorten will launch Labor's Longman campaign in Caboolture on Sunday, a day after Prime Minister Malcolm Turnbull visited the seat.

The latest ReachTEL poll showed the LNP's Trevor Ruthenberg on 51 per cent of the two-party preferred vote, based on 38 per cent of the primary vote and a swag of One Nation preferences.

Labor's primary vote sits on 36 per cent, but won't get much love from Greens preferences with the minor party standing at four per cent.

The federal opposition leader is hoping for a lift from a new policy - spending $1.4 billion over five years to keep in place the energy supplement pensioners and welfare recipients.

Draft laws to scrap the energy supplement for anyone who has become a new pension or allowance recipient since September 20, 2016, are currently before the federal parliament.

Axing the energy supplement will mean a cut of $14.10 per fortnight to single pensioners or around $365 a year, and a cut of $21.20 a fortnight or around $550 a year to couple pensioners.

"If Turnbull gets this legislation through, in the 2020-21 financial year alone more than 592,000 age pensioners will have less in their pockets every fortnight," Mr Shorten said.

Mr Turnbull said the Labor policy showed Mr Shorten was desperate.

"It shows he has given up on bringing down energy prices," Mr Turnbull told reporters in north Queensland.

"He's admitting he's failed before he's even started. He is a quitter."

Mr Turnbull said Labor should be "streets ahead" in the by-elections, but voters were marking down Mr Shorten.

Labor appears on track to win three by-elections, in Perth, Fremantle and the Tasmanian seat of Braddon on July 28.

Labor frontbencher Jim Chalmers said the LNP had won six out of eight elections in Longman and it would be "very difficult" for Labor to retain it, given that One Nation was preferencing the LNP.

"It will be a squeaker - we might not even know (the result) this time next week," he told ABC TV.

A new poll taken in Braddon shows Labor on 52 per cent of the two-party vote with about two-thirds of voters expected to preference the opposition over the government.

The Liberals are not standing candidates in Perth and Fremantle.

The Centre Alliance's Rebeckha Sharkie is widely tipped to retain her South Australian seat of Mayo against a challenge by the Liberals' Georgina Downer.

Liberal senator Eric Abetz said history showed by-elections tended to swing against the government of the day.

Winning Mayo and Braddon would be "exceptionally difficult tasks", he said.

"If we do happen to pick up one of those seats it will be a history-making occasion," he said.

Mr Turnbull is travelling to Tennant Creek on Sunday to get a first-hand view of social and economic problems in the remote Northern Territory town.

Australian Associated Press