Prime Minister Malcolm Turnbull has opened up a fresh front on the industrial relations battleground, proposing new laws to jail union officials and employers who make illegitimate secret payments.

Mr Turnbull and Employment Minister Michaelia Cash today unveiled plans to penalise those found to have made payments other than for clearly legitimate purposes.

The move would make it a criminal offence, punishable by up to ten years in prison and $900,000, for union officials and employees to make or receive payments of "corrupting intent".

Sentences of up to two years and $90,000 would apply for other illegitimate payments.

The proposed new laws would require full disclosure of all payments.

Mr Turnbull said it is the "solemn, legal, moral [and] fiduciary duty" of trade unions to act in the best interests of members.

"We have seen through the Heydon royal commission and subsequently, the way unions have let their members down - how big unions have traded their rights away in return for payments," he said.

"The law applies to all Australians, and it applies to unions."

Senator Cash said there was no consistency across Australia's bribery laws and the offence was often difficult to prove.

"Employees should be aware and should have full knowledge of any payments that are made between their employer and a union," she said.

"It is wrong and compromises the integrity and lawfulness of the workplace."

The pair described their announcement as a test for Opposition Leader Bill Shorten.

Mr Shorten introduced a bill this morning to try and stop future cuts to penalty rates, after the Fair Work Commission's decision to align Sunday rates in the hospitality and retail sectors.

"What I say to the prime minister is use whatever distraction that you think is necessary. Use every possible dishonest distraction you have in your book. Put up whatever story you want," he said.

"But on this issue, when it comes to defending working families in this country, the living standards of working families, we will not be deterred or put off."