A senior Labor frontbencher says Bill Shorten will lead the party to the next federal election irrespective of the results of the Super Saturday by-elections.
Labor is expected to retain the seats of Perth, Fremantle and Braddon, but is behind in the Queensland seat of Longman ahead of the July 28 by-elections.
The party is not contesting the South Australian seat of Mayo, where the Centre Alliance's Rebekha Sharkie is likely to beat the Liberals' Georgina Downer.
Labor's Brendan O'Connor said the party was confident of doing well in Longman, but admitted it was a "tough contest" given One Nation was preferencing the LNP.
Asked on Sky News how a loss would impact on Mr Shorten's leadership, Mr O'Connor said: "Bill Shorten will be leader at the next federal election."
"The last election campaign, the full contest, he won 14 seats and took us within a whisker of winning the election," Mr O'Connor said.
He said Mayo would be a test for Prime Minister Malcolm Turnbull, as it is a "blue-ribbon, safe Liberal seat".
"When you talk about tests for Labor, there are tests for Malcolm Turnbull and Mayo is a test for him."
Liberal frontbencher Josh Frydenberg dismissed any pressure on Mr Turnbull, given no government has won an opposition seat in a by-election for 100 years.
"These by-elections will be close, but history goes against the coalition so we are very realistic about our chances," Mr Frydenberg told ABC TV.
He said the polls showed Mr Turnbull was "way ahead" of Mr Shorten as preferred prime minister.
Asked whether an early federal election was on the cards if the Liberals performed well, Mr Frydenberg said: "The prime minister has made it clear he is expecting the election to be next year and nothing I've heard would changed that prediction."
"The reality is we are trying to climb Everest in winning these by-elections."
Mr Turnbull said the by-elections were a contest of two alternative visions.
"We are for lower taxes, more investment, more jobs, higher wages, stronger growth. Shorten is for higher taxes, less growth, fewer jobs, lower wages and higher prices for electricity," he told reporters in Townsville.
Mr Shorten told a campaign launch in Longman it was not about him or the prime minister.
"On his flying visit here yesterday (Mr Turnbull) said 'Bill Shorten' 11 times, but he didn't mention the word 'schools' once ," Mr Shorten said.
"I don't actually think this by-election is about him or me ... it's about you, it's about your families."
