Greens play mind games with Labor

It should have been a good day for Bill Shorten.

Head down to Geelong in the safe Labor seat of Corio, pledge $59 million to help jobless automotive workers and take a free kick against the Turnbull government for destroying the car-making industry.

It sounded good right up to the moment the Labor leader opened up his press conference to questions.

Enter the Greens.

In a move squarely aimed at wedging Labor, the minor party earlier on Monday announced a plan to enshrine weekend penalty rates in law.

It was the latest instalment in the mind games the Greens have been playing with Labor ever since Malcolm Turnbull called the July 2 election.

Shorten has been walking a fine line on the issue for weeks, especially since he was enticed into telling a Melbourne radio station that Labor would respect a Fair Work Commission ruling on Sunday penalty rates for retail and hospitality workers.

The commission might or might not make that ruling before the July 2 election.

For Labor, a decision before polling day to reduce Sunday rates to the same rate as Saturday is problematic.

That's because it's running campaign advertisements stating it would "keep weekend penalty rates".

Shorten was reluctant to specifically talk about Sunday rates when quizzed by reporters, preferring to say Labor would protect "our penalty rates system".

He also warned the Greens were playing with fire.

Legislating penalty rates was akin to "loading the gun for a future conservative government to "pull the trigger" and abolish them.

Shorten wasn't helped by some of his senior colleagues, including workplace relations spokesman Brendan O'Connor, who declined to say "yes" when asked seven times whether he supported his leader's past statements on the issue.

Nor could O'Connor guarantee the commission wouldn't cut penalty rates in the term of a Labor government.

The Greens argue that Labor talks tough on protecting weekend rates but won't do anything other than that.