Meat workers claim they are not allowed to wear their "jobs that count" union t-shirts to and from work because they are "intimidating".
Spokeswoman for the Meat Workers Union Darien Fenton says workers were told the shirts "were like gang insignia" and anyone wearing one would be sent home.
She says the workers do not wear the green union t-shirts while on the shop floor, so the order only applies to clothing worn into and out of the plants.
Affco's general manager Rowan Ogg says there is no company policy that governs what workers wear to and from work, and there's no company-wide ban on green shirts.
But he says when workers "use any clothing in any way to incite intimidation and divisiveness within the workforce on site, such as gang insignia, then it's up to individual plants to raise it with those concerned and act appropriately".
Mr Ogg confirmed that rule could include union t-shirts "when combined with accompanying intimidatory behaviour by those wearing them".
Employment lawyer Maria Berryman says in the absence of any employment agreement policy or provision, there is no such law which governs what is acceptable to wear to and from work.
She says it's up to the court to decide what clothing can be worn on a case by case basis.
Ms Berryman says the union members could argue that the policy contravenes their human rights, with the freedom of expression and freedom of association.