First Union says its members who are Woolworths staff aren't happy at having to pay for their own Disney costumes as part of a promotion at the supermarkets - but the chain says it's completely voluntary.
Woolworths is running a new promotion in which customers are given cards featuring Disney characters.
As part of that, staff are being asked whether they want to dress up as Disney characters - though they must provide the costumes themselves.
The union said staff were told were to dress as accurate Disney, Marvel and Star Wars characters with licensed Disney clothing, and were not allowed to dress as DC characters or mix their costumes.
Staff have been involved in industrial action with the company over pay and staffing levels.
First Union national secretary of retail and finance Rudd Hughes said the union had heard from members that the majority would not participate.
He said the promotion was running for a week. "People enjoy dressing up to get out of uniform but it appears employees have to pay for the company's promotion, which seems a bit about-face."
In a statement, Woolworths said it was not making any team members dress up.
"This is a voluntary thing that many of our team have done before for various occasions. Team who don't want to take part will just wear the uniforms - that we supply at no cost - as usual. It's disappointing the union has chosen to misrepresent this, especially as we have returned to talks today."
Nearly 10,000 union members who are staff at Woolworths voted for industrial action that began on Tuesday last week, with staff wearing strike stickers until Friday and members at ten stores handing out "receipt"-style flyers.
A media and social media strike continues. Hughes said the company had policies that meant that staff who spoke to media or posted on social media could face disciplinary action.
Christchurch duty supervisor Michelle McKenzie said many staff could not afford to cover their own living expenses comfortably.
"The request for us to design a Disney-accurate costume from our own back pockets was seen as quite ridiculous," she said.
"It makes us feel like the strike action is falling on deaf ears. We don't want to wish upon a star - we want a living wage, safer staffing levels and penalty rates for nights and weekends."