Police were called after union supporters began approaching customers at the entrance of the store, asking them not to shop there while the strike was on.
About 20 Bunnings staff and supporting unions gathered outside the store at 11am yesterday after a ballot approved strike action.
First Union organiser David Bristow said the strike, which followed a series of actions by union members across New Zealand, was part of opposition to a company plan meaning workers would lose the power to set their own rosters.
Mr Bristow said under Bunnings' proposal, a worker's start and finish times, and work days, could change at a manager's whim.
Members in Christchurch were also on strike yesterday.
A demonstration outside the store started without incident but police were called after the move to approach shoppers.
While that was happening, a store manager was welcoming customers and assuring them the store was open.
He urged police to move the demonstrators on.
First Union organiser Shirley Walthew, of Dunedin, said her legal advice was the protest was not against the law, but police at the scene had asked that protesters not physically approach customers.
They were allowed to continue to speak to them.
The manager at the scene would not comment, instead referring questions to Bunnings' national office.
Bunnings declined to comment on the event.
Responding to earlier Otago Daily Times questions about the dispute, Bunnings New Zealand general manager Jacqui Coombes said team members normally received notice of their proposed rosters at least four weeks in advance.
''This will not change. If there are times when a team member has other commitments or challenges (for example, day-care arrangements), then of course we will work with them to best accommodate their needs, just as we do now.
''Each store sets its own rosters.''
Police said there were no arrests at the demonstration.
