Fears have been raised that a town could miss out on thousands of cruise ship visitors due to a lack of parking.
Flood alleviation work in Beaumaris means the castle's coach park is currently out of action.
The local Beaumaris council and Anglesey County Council has failed to come up with an alternative site.
Anglesey cabinet member Bob Parry said Beaumaris's future as a destination for cruise passengers could be jeopardised unless a solution was found soon.
Beaumaris has been a popular stop during land excursions for cruise ship passengers docking at Holyhead.
But the castle coach park is currently being used as a works compound for the flood improvements, and will later be used as a diversionary route when the B5109 is closed as part of the project.
Mr Parry said the county council's efforts to secure part of Beaumaris Green as an alternative coach park had come to nothing.
"In the absence of any real alternatives, I would urge the town council to work with us to ensure that Beaumaris continues to benefit from vital cruise trade," he told the Local Democracy Reporting Service.
However, Beaumaris town councillor Stan Zalot said he did not think the green spaces were suitable for coaches.
"We've only just spent £10,000 on their upkeep due to damage from cars, so who knows how they'll be after dozens of buses park there," he said.
A special meeting of Beaumaris Town Council has been called for Tuesday night in an attempt to find a solution.