The comments were made in a statement the day after the BBC reported workers at Scotland's largest container port are set to go on strike on Tuesday in a row over rotas and pay.
The spokeswoman insisted changes to shift patterns were needed to reflect the needs of customers.
But the Unite union has said the new rotas amount to a "de facto pay cut".
A spokesman for the Port of Grangemouth said: "The strike action proposed by Unite the union is unjustified.
"We are proposing alterations to shift patterns in response to the changing needs of our customers, whose vessels call at the port seven days a week.
"Our staff and their union accepted the need for such flexibility, and that shift patterns may require to change in the future, when this element of their employment contracts was agreed in 2011.
She added: "We have decided to close the port's quayside container operations from midnight on Monday 14th March. All other operations at the port will remain open.
"We sincerely hope that our staff, and their union, will cancel this strike and work with us to implement the changes necessary to enable us to meet the changing demands of our customers."
The union Unite has said all but two of 75 "operatives" based at the Port of Grangemouth voted for the action in a ballot.
The workers include crane drivers and loaders.
It is understood that about 20 engineers who are also based at the site are not involved in the action, which is due to start at 00:01 on Tuesday.
Unite said the action had been called after port owner Forth Ports announced changes to shifts.
Grangemouth handles more than 150,000 containers annually, with daily sailings to Rotterdam, Antwerp, Felixstowe and Hamburg.
A spokeswoman for Forth Ports has called the planned Grangemouth strike "unjustified".