Stretched limousines may fail strict new emission standards being imposed in Leeds and Wakefield, councillors have been told.
The luxury vehicles could be charged up to £50 for entering Leeds, once new clean air zone policies are brought into force from January 6 next year.
Some lorries, coaches and taxis will fall foul of the legislation, which is designed to cut the number of highly polluting vehicles on the city's roads.
There are no plans yet to introduce such fees in Wakefield, but the district council is banning older makes of some vehicles in a bid to cut emissions.
But the suggestion that larger limousines, which are currently unregulated, could be affected by new rules was made at a licensing committee meeting in Wednesday.
Wakefield Council licensing officer Kevin Straw said: "We can only licence vehicles of up to eight seats.
"Anything above and beyond that becomes a small minibus.
"It's not a simple subject because a lot of councils, including this one, but perhaps more especially Leeds, are introducing new standards for emissions.
"A lot of these limousines won't meet those new requirements I'd have thought.
"It's a tricky question of how we bring those vehicles into the licensing fold."
The committee agreed to seek guidance from the Department of Transport over the matter.
Councillor Margaret Holwell said: "A lot of these vehicles are not always very safe. It's a bit of a grey area.
"The government should be giving some direction on this. It's their responsibility.
"We need to know what's going on in our area and we need an overall policy I think."
Elected members in Wakefield are also considering whether or not to adopt new statutory guidance, issued by the government, for the taxi industry.
A national register for all private hire drivers who've had their licence revoked is one of the new measures that could be introduced.
The guidance does not have to be adopted by local authorities, but they have to offer sound reasons for not doing so if they decide not to implement any of the guidelines.
Local Democracy Reporting Service