Ian Paisley has been accused of "hiding behind parliamentary privilege" after the DUP MP accused a Belfast-based solicitor of pursuing a "vindictive" legal action against a former RUC officer.
The North Antrim representative made the remarks in the House of Commons yesterday during a debate on the British government's controversial legacy bill.
Mr Paisley described the solicitor acting on behalf of the family of Colum Marks as a "certain shameful snake-oil salesman", before questioning the lawyer's legal qualifications.
It is understood Mr Paisley was referring to Gavin Booth, a fully qualified solicitor and a partner in Phoenix Law.
Under parliamentary privilege, MPs are protected against civil or criminal liability for actions or statements made in the course of their legislative duties.
Marks, a 29-year-old IRA man, was fatally wounded in disputed circumstances in Downpatrick, Co Down in April 1991.
In May, it was announced that the former RUC man involved in the incident – known as Officer B – would not be prosecuted.
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Police claims that Marks was armed and refused to stop when an attempt was made to arrest him are disputed.
His family has sought a review of the Public Prosecution Service's decision not to prosecute the officer, while they are also awaiting the outcome of a Police Ombudsman's investigation into the incident.
Mr Paisley, who in 2017 called for the officers involved in the killing to be given medals, said there was "going to be another trial—another attempt to drag that officer, known as Officer B, before the courts".
"That officer has long since retired. He has another family and is trying to live his life, yet this continues to hang over him," the DUP MP said.
"We have a certain shameful snake-oil salesman of a legal practitioner saying that he is going to take this person – this 'RUC murderer' –back to court on behalf of the Marks family. That is vindictive and it is ongoing, and those matters do offend."
In a statement, the Law Society called for "attacks on lawyers made in relation to this bill to cease immediately".
"Solicitors provide vital support to victims and survivors of the Troubles to access truth and justice and should not come under attack for doing their jobs," the lawyers' body said.
South Down MP Chris Hazzard condemned Mr Paisley's comments, saying "the inferences made are dangerous and hark back to darker times".
“MPs should not be hiding behind parliamentary privilege to engage in commentary of this type," the Sinn Féin MP said.
“All public representatives have a responsibility to be mindful of their language in the course of the ongoing legacy debate and to consider the impact their words and actions can have on the safety of legal professionals as well as on victims and their families."
In 1999, Ian Paisley Snr used parliamentary privilege to wrongly accuse Co Armagh farmer Eugene Reavey of being responsible for the Kingsmill massacre, some 23 years previous.