Mick Wallace TD accused of defaming the North's First Minister, will not be deterred because of the threat of legal action, his lawyer has said.
Mick Wallace is being sued by Peter Robinson over allegedly defamatory comments posted on Twitter.
In a statement, Gareth Noble, a solicitor for the Wexford Independent TD, said: "Deputy Wallace has a proud record of highlighting important matters in the public interest in relation to issues which demand transparency, openness and accountability.
"He shall not be distracted or deterred from continuing this work by the threat of legal action."
Earlier this year, Mr Wallace used parliamentary privilege to make explosive allegations of a political pay-off linked to a massive £1bn property deal between Nama and a US investment firm.
He claimed £7m in an Isle of Man bank account was "reportedly earmarked for a Northern Ireland politician or political party".
Nama and all private firms involved in the Northern Ireland assets sale have denied wrongdoing.
Mr Robinson has also emphatically denied any link and said no one in his family or the Democratic Unionist Party (DUP) hoped to benefit "one penny" from the huge property deal.
The allegations have sparked probes by specialist detectives and politicians on both sides of the border.
The statement from Mr Wallace's legal team added: "It is not considered that the commentary referred to on social media was in any way defamatory."
Earlier, Mr Robinson, who has temporarily stood aside as First Minister of Northern Ireland because of an ongoing crisis at Stormont sparked by the murder of a man by Provisional IRA members, confirmed his lawyers had been instructed to pursue the case.
Speaking from Stormont Castle, the DUP leader also issued a stark warning.
"It is a matter of some importance that people who want to make up stories, are challenged on the stories that they make up and my legal team will be looking after that. He (Mr Wallace) will not be the last."
His solicitor Paul Tweed, who has represented celebrities such as Britney Spears, Harrison Ford and Louis Walsh, said Mr Wallace had been "put on notice".
However, confidentiality issues have prevented Mr Tweed from the discussing the case any further.
"I can confirm that Mick Wallace has been put on notice of legal action in relation to a highly defamatory tweet," he said.