A 'stop the bullying' rally is planned by unionists protesting about alleged treatment of workers at SkyCity Entertainment Group's Auckland property, but the business says the gathering has taken it by surprise.

SkyCity says it knows nothing about the planned rally, has contacted Unite and has a zero tolerance of bullying.

'Respect for SkyCity workers now! Stop the bullying' rally is an event being promoted on Facebook and planned for 5pm tomorrow outside SkyCity.

"This culture has to stop. One of the best dealers we have had who has won many company awards for excellence has been hounded," Unite union said on social media.

A Unite spokesman said the union had been dealing with a number of cases involving bullying at the company.

But a SkyCity spokeswoman said the business did not know about these issues.

"This is the first we've heard about it - we've contacted the Union to ask them for clarification.

"We have zero tolerance for bullying in the workplace and we have processes in place for people to make a complaint about such behaviour, which we would in turn investigate.

"We have a constructive relationship with Unite, and we would have expected those processes to have been followed, rather than reading about this on Facebook," the spokeswoman said.

The Herald understands SkyCity and Unite are in discussions over contract negotiations