Addressing the Commons on Wednesday, Foyle MP Mr Eastwood said troops “were sent to my city to murder” in 1972 and that the Parachute Regiment has “yet to apologise”.
Thirteen civil rights protesters were shot dead by soldiers on January 30, 1972.
Another man shot by paratroopers during the same incident died four months later, although his death was officially attributed to a brain tumour.
Speaking at Northern Ireland questions, Mr Eastwood said: “Fifty years ago this week the Parachute Regiment were sent to my city to murder 14 people.
“People who were unarmed, marching for civil rights.”
Mr Mercer, the MP for Plymouth Moor View, later raised a point of order in the chamber to say: “The member for Foyle made an extremely incendiary allegation that British troops went to his constituency in the 70s with the express purposes of murdering the people who lived in Derry.
“Now, we all have a responsibility in this place around the language we use. Legacy is extremely difficult to deal with, but what guidance can the Speaker give me... that we can put a stop to this behaviour in [the Commons]?
Sir Lindsay Hoyle acknowledged these are “very sensitive issues” and recalled at the start of Northern Ireland questions he had requested that MPs exercise caution when referring to such matters.
However, he added “nothing disorderly has occurred” as the names of those involved had not been referred to by Mr Eastwood.
Mr Mercer later posted a video of his Commons contribution, followed by a photograph of Colum Eastwood carry the coffin at an INLA funeral.
He added the message: “And here he is carrying the coffin of an INLA terrorist a few years ago.. A sheep in sheep’s clothing, trying to stir up division simply for political gain. Grow up @columeastwood.
“Come join the adults as we try and heal the past, not make a living from it.”
The News Letter has asked the SDLP if Mr Eastwood intended to claim that troops were deployed on Bloody Sunday by Army commanders with the premeditated intention of murdering demonstrators, or if he just mis-phrased the sentence.
No response had been received at time of writing.
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