Federal Labor frontbencher Bill Shorten says his decision to switch support to Kevin Rudd from Julia Gillard was a "tough call", but has made the government more competitive.
Labor appears likely to lose the September 7 election, based on current opinion polling, despite Mr Rudd's return as prime minister in June.
Mr Shorten had helped Ms Gillard seized the leadership from Mr Rudd in June 2010.
"It was a very tough call those weeks ago," he told the National Press Club in Canberra on Tuesday.
"I have no doubt that Kevin Rudd is making us as competitive as we can be."
Mr Shorten said the release of the coalition's costings - expected in the final week of the campaign - would boost Labor's fortunes.
"Politics is not a game of hide and seek, where the coalition hide their policies and the public have to seek them out and the prize if you don't get caught is the government of Australia," he said.
The workplace relations minister says the coalition will junk many of its promises if it wins, and push to scrap penalty rates and broaden the use of individual contracts.
