A union is facing a possible High Court injunction over planned industrial action involving a port's pilots and launch crews.
Unite the union members at Milford Haven, Pembrokeshire, have voted on a possible walkout on Thursday and Friday.
But port managers plan to challenge the legality of the action, which was prompted by a row about pensions, the BBC reports.
Unite representative Allan Card said the union believed the notice served on the port authority was lawful.
He said the union had offered to suspend the threatened action for up to 28 days in order to resolve the matter, adding: "We've worked very hard over the last couple of weeks to try to resolve it, but we're still not in a position where we can actually say the matter is resolved."
Talks are ongoing, but the port authority said it believed there were "some inconsistencies" when Unite members were balloted.
Chief executive Ted Sangster said: "The authority is disappointed that industrial action is planned which could potentially damage the port's reputation, impact on customers and the wider needs of the county".