Micheál Martin has criticised the Taoiseach over his handling of the case involving Dara Murphy and his Dáil attendance record.
It emerged last month the former Fine Gael TD claimed his full expenses, despite being largely absent from the Dáil over the past two years.
He held a role in Brussels over the same period and resigned as a TD last week.
The Fianna Fáil leader says the major issue is Mr Murphy's absence and the impact it has had on his former constituents in Cork North Central.
"I think the Taoiseach has not faced up to the moral issue that underpins the Dara Murphy case," said Mr Martin.
"It's not just about turning up, or fobbing, or those issues - important as they are.
"It really is fundamentally about the representational role of a deputy and the legislative role of a deputy.
"And clearly Dara Murphy didn't fulfil either over the last two years."
Last week Leo Varadkar said Mr Murphy should only
Earlier today, Mr Martin has said he has no intention of reinstating two TDs who were removed from the Fianna Fáil front bench
Timmy Dooley and Niall Collins stepped down from their front bench positions in October after footage of the Dáil chamber showed Mr Dooley appearing to motion his colleague Mr Collins toward his vote button ahead of his absence during votes.