Lawyers for Ulster rugby star Paddy Jackson have launched a defamation action against a senator in the Irish Seanad for social media comments he posted after the acquittal.
KRW LAW has issued an intention to sue Senator Aodhan O'Riordain.
Jackson's lawyers said he had no option other than to resort to the civil courts to "seek protective action" following his acquittal.
Marie Hans, senior associate at KRW LAW, said: "I can confirm we have issued pre-action libel correspondence against a named senator in the Republic of Ireland. The legal action relates to a tweet sent to a number of other persons before it was eventually taken down."
She said the legal team "will not hesitate to repeat similar legal action" against other individuals.
"We are examining carefully every item of social media commentary which seeks to challenge the integrity of the jury's full endorsement of our client's innocence," said Ms Hans.
"High court proceedings will issue shortly in both Belfast and Dublin."