The four-hour stoppages, from 2300 to 0300, will take place every night from Thursday 20 June through to next Wednesday, 26 June.
“We are close to agreement,” Maritime Union of Australia national assistant secretary Ian Bray said.
“However, there remain a few unresolved issues that the workers consider important enough not to walk away from and, as a result, the workers are taking this protected industrial action.
“We emphasize again, however, that we seek to reach agreement on those unresolved matters because we, like PWCS, would welcome a return to getting on with the business of shipping coal to PWCS clients.”
Talks between union members and PWCS have seen more than nine months of negotiations.
The single bargaining unit representing workers comprises the Maritime Union of Australia, the Transport Workers Union, the Electrical Trade Union, and the Australian Manufacturing Workers Union.