The head of the National Bus and Rail Union (NBRU) has said members may have to decide who can and cannot travel on buses, amid public health concerns.
General-Secretary Dermot O'Leary said there is a concern over low numbers of people wearing face masks on public transport.
He also said discussions are ongoing in relation to a lack of protective screens for Dublin Bus and Bus Éireann drivers.
But he told Pat Kenny that lack of clarity around the wearing of face masks is a real issue.
A survey of NBRU representatives has found that on Monday, people were by-and-large adhering to social distancing guidelines.
However by Tuesday, social distancing was reduced and people were ignoring the 'Don't Sit' seat signs on buses.
He said: "The evidence from our survey on Monday was that less than 1% were wearing masks - and this is a concern.
"The debate on masks is varied and it depends who you listen to.
"I see Simon Harris reported in the media overnight saying that they maybe have to re-look at it again.
"The advisory group to the Government at one stage said 'you should wear masks on public transport', but that was changed because NPHET were concerned that medical-type masks would be sucked up by the general population away from where it's needed on the frontline.
"I just think that's insulting".
Minister Simon Harris told Pat Kenny on Tuesday that the issue will be kept under review.
Some 50 countries-plus have made the wearing of face masks compulsory on public transport - while Belgium and France can fine people for not wearing masks.
Mr O'Leary said: "The debate we're not having with the stakeholders, we should be at the table, that is the unions representing workers.
"[We] should be at where these decisions are being made and my concern Pat is this: that at some stage, we're going to have to make some hard decisions as unions in relation who can and can't travel on buses.
"And to be honest with you, that's not our role.
"Whatever happens in industrial relations when there's disputes around pay and the likes, that's one thing.
"But when it comes to public health and the safety of people who both use the service and work in the service, that's an issue that we should be discussing with our expertise entering into the debate - and we shouldn't be waiting for people to hand down dictats to us".
He said policing the wearing of masks could be a problem.
"We've asked the question: is there a role for Gardaí here.
"It is public order in some situations where you're talking about the public thoroughfare, you're talking about train stations."
"And again one of the other concerns we have in the NBRU, and transport workers generally would have, is that the Return to Work Protocol issued last week did not in any way cover transport."
And he said policy has to be very clear on social distancing.
"Certainly there needs to be debate where people who are going to be affected by the social distancing reduction - if that comes - by the wearing of masks, which has to come, there needs to be a major debate on how we're going to all use public transport".
In relation to capacity issues, he said a double-decker bus on average now carries up to 19 people, while trains are down by about 90%.
"We need to find some measures to restore confidence in people and instill confidence in people to use public transport.
"But we can't do that unless we have strict policy and guidelines - and indeed mandatory rules on face masks or face coverings in place".
"The balance that needs to be struck is the return to some type of normal economic activity, and the ability of people to get from A to B".
The NBRU wrote to Taoiseach Leo Varadkar and other party leaders last week, suggesting a number of measures to keep people safe on transport.
This included staggering college and school starting times - as well as staggering starting times of work in office blocks.
"Certainly in terms of the general point about people travelling in enclosed spaces, you can't have one rule for airlines and a different rule for buses and trains.
"There needs to be that debate."