Luke "Ming" Flanagan has said he would resign as an MEP if he was in the same situation as his counterpart Brian Crowley, who has been unable to attend the European Parliament since his re-election in 2014 due to ill-health.
Mr Flanagan said that being present for votes in the parliament was an essential element of an MEP's job.
Mr Crowley is currently in hospital and his Fianna Fáil substitute, Kieran Hartley, recently called on party leader Micheál Martin to intervene. However, the party says it is powerless to act.
Mr Flanagan, an Independent MEP for Midlands-North West, said that in the three years he has been in the European Parliament he has never met Mr Crowley. Other MEPs say Mr Crowley attendance at the last parliament, from 2009 to 2014, was also poor.
"It is up to Brian to decide, but if I were in that position, I would resign," Mr Flanagan told the Neil Prenderville Show on Red FM. "More's the pity that he can't be there. He's immensely articulate."
Mr Flanagan said it would be much better for Ireland if Mr Crowley did attend, as every vote counts and on some occasions votes were very close.
“Obviously this is a very sensitive situation, but this is about our country. It diminishes our impact.”
He said there were 24 committees in the European Parliament, and even with all MEPs attending, Ireland would be represented on fewer than half of them.
“This is very sensitive but it is also very serious. With issues like Brexit we need more numbers at committees.”
Mr Flanagan said he was particularly conscious of Mr Crowley’s position, as he had to miss three months of the parliament when his own wife was unwell.
“It did impact on my work,” he said. “I would not have been able to keep up if I had lost any more time.”
Mr Crowley’s office has previously said he is working while in hospital.
Unable to vote
Mr Flanagan said there was a certain amount of work that Mr Crowley could do while not attending, but he was unable to vote.
“Some issues are very close. One vote can make a difference... If you can do the work without voting, why would we need MEPs?”
Mr Crowley’s spokesman declined to comment on Mr Flanagan’s remarks.
Midlands-North West MEP Marian Harkin told The Irish Times that Mr Crowley's non-attendance was "a matter for Fianna Fáil".
“They should try to speak to him. It’s important that people are here to attend the parliament, to attend committees, to do the work. Otherwise what’s the point in sending us out here at all?”