Mandatory wearing of face coverings on public transport should be introduced at some stage during the easing of coronavirus restrictions, according to the National Bus and Rail Union (NBRU).
The union says a survey carried out among members two weeks ago showed only a small number of passengers were wearing masks or other coverings.
Currently, the Government has recommended that members of the public wear face coverings on buses, trains and trams, but it's not compulsory.
However, the NBRU has written to the Oireachtas COVID-19 Committee suggesting that situation will have to change as restrictions continue to be eased and more people return to public transport.
NBRU General Secretary Dermot O'Leary told Newstalk Breakfast there should be a 'no mask, no board' policy in place at some stage in the process.
He said: "What we need to figure out as a society is what stage that is at - is at stage two, three, four or five?
"In France and Belgium, for example, you're fined if you don't wear a mask on public transport. There are a lot of conflicting messages out there.
"Our members don't want to be in a situation where they have to make a decision whether people have to wear masks or not: it should be clear policy from Government."
Meanwhile, Mr O'Leary said a bus which once had a capacity of 90 passenger currently has a capacity of only 17 due to social distancing measures.
He said: "Slight caveat on the 90 - 67 people can sit on a bus, and 23 can actually stand on a bus.
"What we would be saying... whatever chance we had of going back to some sort of capacity, we wouldn't envisage a situation where people would be standing on buses in the long-term."