The law firm acting on behalf of Paddy Jackson says it intends to sue Senator Aodhan O'Riordain for defamation.
The Ulster and Ireland player was acquitted of rape and sexual assault at Belfast Crown Court earlier this week.
Soon after the verdict was handed down Senator O'Riordain tweeted his reaction but the post was later deleted.
In a statement KRW Law said it has issued pre-action libel correspondence against a named Senator relating to a tweet sent out to a number of other persons before it was eventually taken down.
It adds that it will not hesitate to repeat similar legal action against anyone who sees fit to attack their client and they are looking at every item of social media commentary which seeks to challenge the integrity of the jury’s verdict.
Paddy Jackson, along with rugby player Stuart Olding, were found not guilty of rape earlier this week.
Two of their friends were also acquitted on charges arising out of the same night in June 2016.