Fianna Fail's high-profile Brexit spokesperson Lisa Chambers has become embroiled in the "phantom votes" controversy that has rocked the party.
She has admitted she recorded a vote "in error" on behalf of Fianna Fail deputy leader Dara Calleary during last Thursday's bizarre session in the Dail.
She apologised for failing to disclose this in a radio interview yesterday.
Party leader Micheal Martin has ordered Timmy Dooley and Niall Collins to stand down from the front bench until the Ceann Comhairle has completed a probe.
Fianna Fail TDs privately expressed fury at the mess as Fine Gael ramped up the pressure.
It comes after Mr Dooley was recorded as voting six times, despite not being in the Dail chamber.
Mr Calleary's assigned seat is beside fellow Mayo TD Ms Chambers.
The Fianna Fail deputy leader was not present at the start of Thursday's session as he was doing a radio interview.
Ms Chambers was asked on RTE yesterday whether she had ever voted for a colleague or had a colleague vote on her behalf. She replied: "No, I haven't."
However, she failed to mention the vote she made in error and last night apologised.
She said she inadvertently sat in Mr Calleary's seat and "pressed the button once in error on the first vote".
She added: "No one asked me to do this and when I realised I immediately moved to my own seat."
The record shows a vote in Ms Chambers' own seat as well.
"The vote was lost by a large number, so I did't inform the Teller. It was a genuine mistake and not intended," she said.
"I genuinely believed this error was insignificant and when asked on RTE had I ever voted for anyone else I answered no as I was never asked to vote for anyone else.
"For this I apologise."
Mr Calleary said: "I did not and would not ask any other deputy to vote for me in the Dail."
Ceann Comhairle Sean O Fearghail has ordered an investigation after the revelations about Mr Dooley and Mr Collins.
Both TDs have said Mr Collins had pressed Mr Dooley's voting button in the mistaken belief he was still in the chamber.
Fine Gael Health Minister Simon Harris said on RTE that their explanation was in the "dog ate my homework territory".
Mr Martin asked Mr Dooley and Mr Collins to step down as front bench spokespersons for communications and foreign affairs respectively.
He said he was doing this without prejudice and pending the outcome of the Ceann Comhairle's report.