The Electrical Trades Union (ETU) said 100 per cent of its 100 members taking part in the vote endorsed work stoppages ranging from 30 minutes to 24 hours, which could begin within days.
More than 100 members of the Australian Manufacturing Workers Union (AMWU) also voted 89 per cent in favour of taking strike action, a spokesperson said on Thursday.
The votes come after months of talks with BHP, the world's biggest listed miner, to agree on a labour agreement, with workers seeking improved pay and conditions.
BHP did not immediately respond to a request for comment.
Port Hedland is one of the largest iron ore loading ports in the world and the biggest in Australia.
It is linked to a number of BHP's mines in the Pilbara region and is used for all of its iron ore exports in Western Australia.
The ETU said it was seeking an agreement that ensured parity for workers at the port with the same skills and experience, after they were hired on "wildly disparate" individual contracts.
"We have attempted to negotiate a resolution for more than six months, but BHP's obstructive conduct has meant we don't have anyone to negotiate with," said Adam Woodage, state secretary for Western Australia.
Workers might begin industrial action after giving five days of notice, the union added.
AMWU state secretary Steve McCartney said workers had spent seven months unsuccessfully bargaining with the company.
"Members have had enough," he said.
"They are demanding to be heard and they are demanding a fair agreement."
"More than 100 workers are standing up for fair wages and conditions during a cost-of-living crisis."
