The Finance Minister says he believes the Taoiseach should travel to Washington DC for St Patrick's Day if he gets the invite.
However, Paschal Donohoe doesn't believe Micheál Martin would have to be vaccinated to travel to the US.
With the traditional St Patrick's Day trip just weeks away, it remains unclear whether Mr Martin will fly to DC to meet new US President Joe Biden.
The Taoiseach has said no decision has been made yet, and no invitation has been received to date.
Amid strict restrictions on international travel, Sinn Féin is among the parties saying this year's trip shouldn't proceed.
Minister Donohoe, however, told The Hard Shoulder he thinks the trip would be essential.
He said: “I believe if the White House extends the invitation he should go.
"President Biden is the most powerful leader of a democratically-elected government in the world… if he believes it’s healthy and safe to meet the Taoiseach, the Taoiseach I believe should accept the invitation.
“So many of the different challenges we have coming up, particularly in relation to the economy, are intimately tied into the relationship we have with the US. If we decide we’re not going to take up that invitation, how will we feel if other countries decide they do want to?"
The minister said people are allowed travel without vaccination at the moment.
He observed: "It is all about how you conduct yourself, and being safe while you’re abroad.
"I don’t believe getting a vaccination is a necessity for him travelling, and I think the Taoiseach - like many of us - is waiting for vaccinations to happen within the community before we get an opportunity."
'He must show leadership'
Also speaking on the show, former Irish Senator Billy Lawless said the Taoiseach should ‘absolutely’ go to DC.
He said Mr Martin should also be vaccinated immediately.
Mr Lawless argued: “This is a business trip - essential business trips are allowed.
“Now, more than ever, with the hospitality business on its knees… we need US business and tourists travelling to Ireland, when it’s safe to do so.
“We need the exposure.”
Independent TD Mattie McGrath said he’d ‘100% agree’ with the US trip if these were normal times.
However, he said it shouldn’t happen at the same time as the Oireachtas is likely to be considering new laws to introduce mandatory quarantine for some arrivals here.
He said: “How at the same time are we going to have the Taoiseach getting on a plane to get to the White House?
“It’s the wrong message to send out to the public in general… he must show leadership.”