Not wearing face coverings on public transport 'will be an offence' if Cabinet approves new rules, Transport Minister Shane Ross has confirmed.
He will bring a memo to Cabinet tomorrow calling for masks to be mandatory on buses, train and Luas services.
Minister Ross will tell his colleagues that public transport capacity needs to be increased to 50% as more people return to work.
Speaking on Newstalk Breakfast, He said: "Yesterday there was a sub-committee of the Cabinet, and I brought a memo to them basically saying that public transport - which is absolutely essential - is going to get very crowded in the next few weeks.
"We're getting close to a point of overflow... we've got to do something very serious about it."
Minister Ross said that 50% capacity means it won't be possible to social distance in the same way.
He explained: "As a counter for that and remedy for that, we're introducing mandatory face masks... which we hope will have a very dramatic effect.
"I think everyone will behave responsibly... people are behaving very responsible indeed. But it will be an offence not to wear face masks.
"It's been very striking that people haven't been keen to wear them... that's really one of the reasons why we have to make it mandatory."
He suggested there can't be "options" when health and life are at stake, so it has to be enforced.
He suggested: "It is so important we don't let our guard down - we've done so well on coronavirus in public transport terms and other terms nationally. I think it would be a great pity if there were areas where people become very lax about it."
The Transport Minister also confirmed that air bridges between Ireland and other countries where the virus is under control are being 'actively considered' - but no decisions have yet been made about any country.
The planned rule changes have been welcomed by those who've been campaigning for mandatory face coverings on transport.
Kingston Mills, Professor of Experimental Immunology at Trinity College Dublin, said the measure should have been introduced "weeks ago".
Dermot O'Leary, general secretary of the National Bus and Rail Union (NBRU), welcomed the move after his union repeatedly called for face coverings to be made compulsory on buses and trains.
He said: "It's good to see that the outgoing minister, who has been severely criticised for doing everything else in his brief except transport, has done something now directly related to transport.
"If I'm going to criticise somebody, I have to be in a position to acknowledge if they do something as well as well. I have to acknowledge it's the right move by the outgoing minister."