Another Australian firm is being accused of using changes to employment law to manipulate the contracts of New Zealand workers.

Orora Kiwi Packaging workers in Auckland, Christchurch and Hastings begin two weeks of an overtime ban today, to protest what they see as their employer's attempt to take away important worker rights.

EPMU postal workers organiser Joe Gallagher can't understand why the Australian owned company wants to attack its kiwi workers.

"This is not a distressed company. This company is returning good dividends to its shareholders and returning good profit."

Gallagher says the changes relate to leave requests, service pay and staggering meal breaks.