Labor has moved to target Malcolm Turnbull and Kelly O'Dwyer's banking careers as it questions the Coalition's motives on reform of Australia's $2.6 trillion superannuation industry.

Days after the Productivity Commission released an interim report questioning the use of default funds linked to industrial relations agreements, Labor's employment and workplace relations spokesman Brendan O'Connor accused the Financial Services Minister of "palpable loathing" for employer and union-backed industry super funds, and suggested the Prime Minister couldn't be trusted to implement the findings of the final report.

Shadow treasurer Chris Bowen has refused to say if Labor will support the proposed independent "best in show" list of high-performing funds recommended by the commission, or say if the opposition would support moves to make it unlawful to force workers into funds linked to industrial agreements.

"We support industry super, and Labor, of course, being the authors and architects of having a superannuation scheme in this country, are very sceptical of the motives of the government," Mr O'Connor told ABC TV on Sunday.

"I mean, we've got the former banking executive, minister O'Dwyer and a former merchant banker, the Prime Minister, oversighting this arrangement. We don't trust their motives, quite frankly, given their conduct in recent years as ministers."

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Ms O'Dwyer was a National Australia Bank executive from 2007 until 2009, while Mr Turnbull helped found investment bank Turnbull & Partners in the 1980s, later becoming Goldman Sachs Australia chairman and managing director.

Asked if Labor was open to the decoupling of super from industrial agreements, Mr O'Connor said industry funds systematically outperformed retail funds, but the party would await the final report.

He accused the government of weakening existing measures by refusing to appoint panel members to oversee default funds within the Fair Work Commission.

"We're just not going to respond to all of these matters, but I make the point, we've had a minister who has a palpable loathing for the highest performing industry funds.

"So when you've got such an ideological predisposition against the best-performing funds, no wonder we can't get clarity from the government in relation to what they want to do."

Mr O'Connor said Bill Shorten's leadership remained secure despite new polling showing Labor behind in two key super Saturday byelection races.

The government would reclaim the Queensland seat of Longman and the northern Tasmanian seat of Braddon if new ReachTel polling results are replicated when voters go to the polls on July 28.

Sky News reported the Coalition had a 52-48 per cent lead over Labor in Longman and a 54-46 per cent lead in Braddon.

Labor's Susan Lamb and Justine Keay resigned in the seats because of dual citizenship.

No government has won a seat from the opposition in a federal byelection since 1911.

Mr O'Connor said Labor's caucus was behind Mr Shorten.

"Well, I think that firstly, Bill is absolutely secure in his position, he is doing a great job," Mr O'Connor said.

"He brought us very close to an election win when everyone had written us off at the last election, almost in one term, and we are a united, focused opposition, putting forward plans for Australia's future.

"I think our policies, as presented, make us very competitive at the next general election. We take nothing for granted but Bill Shorten is our leader and doing a very good job."

Workplace Minister Craig Laundy said the government was hopeful of winning at least one of the seats, but was expecting a hard-fought campaign.

"We have to be extremely cautious. No government, I think, since 1911 has won a byelection for a seat it did not hold," he said.