Car ferry operators are awaiting clarification about the workplace smoking ban as it applies to them after it was established that it doesn't apply to fishing crews once they are over 12 miles offshore.
The law may not apply on the high seas outside the territorial limit, according to marine sector representatives.
"We have enough problems anyway without having this one to contend with," said Mr Lorcan Ó Cinnéide, of the Irish Fish Producers' Organisation (IFPO).
Fishing vessels are both workplaces and domestic environments, and, as such, may be subject to the ban in inshore waters.
However, the Department of Communications, Marine and Natural Resources has given no special direction to the industry, added Mr Ó Cinnéide.
Nor has the Naval Service been asked to police the smoking ban within 12 miles.
"Our primary role is fishery protection, and our powers are confined to a limited area of legislation otherwise," Lieut-Cdr Gerry O'Flynn, Naval Service spokesman, told The Irish Times.
The majority of vessel boardings undertaken as part of fishery protection duties occur outside the 12-mile limit in any case, he added.
Smoking is "almost gone" on Naval Service ships under measures introduced several years ago, Lieut-Cdr O'Flynn said. "It has been confined to very designated upper deck areas for some time."
However, some passenger ferry companies are awaiting clarification from the Department of Health and from the Health and Safety Authority on the legislation.
"We have been in touch with both bodies, but no one has come back to us," said Mr Eamon Hewitt of Stena Line. Until such guidance was provided, there would be no change to current arrangements on his company's ferries.
Stena's fleet is registered under the British flag, however, and it has staff employed in Britain.
"There is a question-mark as to whether this can apply to ships which do not sail under the Irish flag."
P&O Ferries is also registered under the British flag, while vessels with Irish Ferries are on the Irish register.
A spokesman for Irish Ferries said that it intended to implement the ban fully on its vessels.