Local leaders in Merseyside have raised worries that confusion over acceptable ID in elections could exclude some people from voting.
Voters must have photo ID when they head to the polling stations for the May local council elections which includes national bus passes for people aged 65 and older.
But the Merseyside’s 60+ local bus pass is not on the list of acceptable documents.
It means one of the bus passes issued by the same authority with the same security checks is acceptable while the other is not.
Following last year’s Elections Act voters must present photo ID from a list of acceptable documents to vote in person at local and general elections.
The Electoral Commission guidance says one of the documents that can be used is an older person's bus pass.
Tom Crone, leader of the Green group on Liverpool City Council, said: ‘We are still being approached by residents who aren't sure if their ID is valid.
‘The fact that one type of bus pass is valid but another isn't means that people could be turned away from polling stations due to an honest mistake.
‘Some people might not have the time to return and will therefore be denied their right to vote.’