There's a 'clear-cut case' that secondary school students should have to wear masks in the classroom, according to former HSE chief Tony O'Brien.
He is accusing the Department of Education of "dithering" on the issue, and has signed a petition calling for the measure to be introduced.
Face coverings will be compulsory in shops and shopping centres from next Monday, with the same rule already in place for public transport.
Health Minister Stephen Donnelly has said NPHET is waiting for a European report before deciding whether masks will be required in schools.
Speaking on Newstalk Breakfast, however, Mr O'Brien said he believes we'll see masks in secondary schools become necessary "very quickly" if the rule isn't introduced ahead of reopening.
He observed: "It's going to be a slightly odd situation where they're going to have to wear masks to travel to school on public transport, then when they're in situations which are likely to be equally crowded they will not be required to wear them.
"Many of those students are going to [have] vulnerable other members of their families at home... some of the teachers might have vulnerabilities, some of the students will have vulnerabilities.
"I think it's just a matter of time until we're going to see a requirement for masks - it would be better just to get on with it and make it clear at this stage."
Mr O'Brien said he is specifically supporting the call for masks at second level, as there's a "different set of circumstances" when it comes to younger children.
He said: "Many of [them] are aware of the seriousness of the situation, but probably wouldn't be able to cope where they're expected to maintain full social distance or wear masks.
"There is plenty of room for consideration as to what is and isn't appropriate at level - but I think at second level it's a clear cut case that masks should be there."
'We need to get on and stop dithering'
Mr O'Brien stressed there are "important exceptions" for people who can't wear masks.
However, he said outbreaks in schools would mean "quite serious" consequences for students who've already lost months of education.
The former HSE chief said: "Secondary students are wearing masks when they go shopping, when they go on trains, when they go on buses and in many other social situations.
"I don't think they'd find it at all strange to be asked to do so in schools - it may even provide them with additional reassurance when they're going back."
According to Mr O'Brien, we're going to be living with COVID-19 perhaps for years - so there is now a need to get on with making 'straightforward decisions'.
He said: "I think this is a further case where we've seen further dithering from the Department of Education - they hummed and hawed about what they'd do with the Leaving Cert... now they're humming and hawing about this.
"I think they just need to get real and get on with it... and I suspect there would be widespread public support if they were to do that."
He suggested the Department of Education is the one department which has "distinguished itself by its inability to make decisions and make them quickly" during the pandemic.
Also speaking on Newstalk Breakfast, Health Minister Stephen Donnelly said European health officials "may come back and recommend in secondary schools, for example, or over a particular age, that face masks should be worn".
However, he said that officials don't know what the report will say, so they're still waiting to see it before any decision is made.