Injecting $200 million into Australia's pathology system will make sure tests for cancer patients stay free, as Labor says the system is at breaking point.
But the coalition argues Labor's promise is just pumping money into pathology companies' coffers, as bulk-billing rates have improved to above 99 per cent.
The Medicare rebate for pathology has been frozen since 2003, but Labor and coalition governments have offered incentive payments to bulk-bill since then.
But the industry now says the top-up payments can no longer cover the costs, so Labor's funding ensure tests stay free for older Australians and cancer patients.
"We accept the argument that Australian pathologists have put to us, that the system is near breaking in terms of bulk-billing," Mr Shorten told reporters in Adelaide on Tuesday.
"Without a significant investment of new funds we could be jeopardising the wide take up of bulk-billing for pathology tests."
Australian Pathology chief executive Leisel Wett said if people avoid tests because of the cost, diseases will get diagnosed later and at greater cost to the taxpayer.
"Without adequate funding, pathology services will be forced to stop bulk-billing," she said.
But the coalition says 99.3 per cent out-of-hospital pathology tests were bulk-billed last year, up from 97.3 per cent in 2013.
Labor's health spokeswoman Catherine King said 140,000 Australians aren't getting pathology tests due to the cost.
Mr Shorten campaigned in the Adelaide seat of Boothby, which Liberal MP Nicolle Flint holds on a 2.8 per cent margin.
The Labor leader has visited a series of Liberal electorates in the first six days of the campaign, as he targets the seats he needs to win power.
On a visit to a Westfield in Oaklands Park, Mr Shorten met shoppers and diners, posing for selfies and shaking hands.
Local resident Anne Murphy got a picture with Mr Shorten, and declared herself "a fan".
"I like him. He's not got a lot of charisma, but I prefer a politician that's not full of ... like, the Trump type," she told reporters.
Despite getting a small benefit from franking credits, Ms Murphy agreed with Labor it's time for the cash handout to end.
"Franking credits are not something we need, we haven't earned them," she said.
Mr Shorten also ruled out any new or increased taxes on superannuation, despite super changes being part of Labor's policy platform since the last election.