Essentially that meant workers' shifts could be chopped and changed with just two weeks' notice.
The new contracts meant workers could be forced to work a six-day week and split shifts and Bunnings was planning on a two-week roster system
"Workers across the country are going to resist this attempt to make their jobs insecure," Ms Gray said.
Outside Bunnings Warehouse in Hastings workers held placards and chanted, "Stand up, fight back."
"While the company is claiming it doesn't intend to make 'wholesale changes', if this is true then why are they proposing a collective agreement that will do just that?" Ms Gray said.
"The workers who are striking today are calling on Bunnings to offer an agreement that respects their rights. They want an agreement that's fair."
In April McDonald's workers staged a similar strike in protest of zero-hour contracts.
McDonald's and Unite Union then came to an agreement and the fast-food giant backed down from the proposal.
Workers were then guaranteed 80 per cent of the average hours worked over a three-month period.
The agreement was touted as historic for the workers' union. Unite called on the Government to turn the decision into law for other workers in the country.