Federal Labor leader Bill Shorten has returned to work energised for an election fight with Malcolm Turnbull over the GST.
But questions over unions continue to shadow the opposition leader.
Making his first public comments on the trade union royal commission's report, released during the final week of 2015, Mr Shorten admitted it did find examples of "bad behaviour within some parts of the union movement".
"I despise thievery, I despise people taking money from union members," he told reporters on Tuesday.
However, the former union leader said the case had not been made for re-establishing a building industry watchdog, which the government wants to pursue.
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Legislation to create the Australian Building and Construction Commission is expected when parliament resumes next month.
Mr Shorten said such a watchdog would create a different set of rules for construction workers to everyone else.
But Labor would study the recommendations and the government's final response when it's released, and its push to again set up a Registered Organisations Commission.
"We have got to fight corruption wherever we see it, not just in unions, not just in corporate Australia, but in every aspect."
Mr Shorten kicked off the election year campaigning in the NSW bellwether seat of Eden-Monaro.
It is the first stop of a three-week tour of the country during which he'll focus on penalty rates, health and the GST.
The opposition leader challenged the prime minister to a public debate over hiking the GST.
He wants to take on his counterpart at the National Press Club in Canberra, daring him to "turn up and put the case" for increasing the tax from 10 to 15 per cent.
"If Malcolm Turnbull's fair dinkum, he'll front up.
"Labor will be on their case to make them rule it out or we'll fight the election on it."
Cabinet minister Simon Birmingham dubbed the opposition leader "grossly irresponsible" for ruling out changes to components of Australia's tax system.
The Turnbull government was taking a "mature and sensible" approach through its tax reform white paper which would analyse the entire system, he told reporters in Sydney.
