The one percentage-point shift is not statistically conclusive, given the poll only surveyed 1,609 voters.
The prime minister still leads Mr Shorten as preferred prime minister. Mr Shorten’s personal approval rating fell one point to 32 percent, while his already-high disapproval rose two points to 57.
That puts him on a net approval of negative 25, compared with his rival’s negative 6.
Labor punished for tax backflip?
The poll comes after Mr Shorten on Friday was forced to backflip on his promise to reverse tax cuts for medium-sized businesses, following a meeting of the shadow cabinet.
But the poll is unlikely to reflect a public backlash. The questions were framed before the reversal, and the poll’s publisher concedes only “some” of those polled were asked after the Friday announcement.
Earlier in the week, the Labor leader answered a reporter’s question and confirmed that “yes”, a future Shorten government would unpick recently legislated tax cuts for businesses with annual turnovers between $10 and $50 million.
But many in the party were unhappy with the decision, which allowed the Turnbull government to blast the opposition for attacking smaller, family-owned businesses like construction firms and small retailers.
Mr Shorten announced the back-down on Friday morning after a shadow cabinet meeting in Sydney.
Businesses that turn over up to $50 million will keep their existing tax cut down from 30 percent to 27.5 percent, but would not get the future years of cuts down to 25 percent under a Labor government.
Labor also opposes the Coalition’s ongoing attempts to pass the reduction to 25 percent for all businesses, regardless of size.
“The shadow cabinet rolled him on a fundamental economic policy, it was an embarrassing humiliating backflip for Bill Shorten,” foreign minister Julie Bishop said on the weekend.
Labor said the reversal was based on new modelling data from parliament’s independent costing agency that showed the medium-business tax cuts would cost less than was “previously expected”.
At a Labor conference on the weekend, Mr Shorten focused on cuts to penalty rates that kicked in on July 1.
“Your penalty rates will always matter to me and Labor just as much as the PM's giveaway to the big banks and multinationals matters to him and the Liberal Party. We will fight,” he said.
Mr Shorten also told Labor’s NSW state conference he would deliver $6 billion in federal money for rail projects in Western Sydney if successful at the next election.
Support for Pauline Hanson's One Nation sits fixed at 6 percent – about half the support recorded at the party's peak.