SDLP leader Colum Eastwood has protested against swearing allegiance to the Crown in the Commons.
Completing the swearing-in process as he took his seat for Foyle, Mr Eastwood said his “true allegiance” is to the people of Derry and Ireland.
It comes after fellow SDLP MP Claire Hanna submitted a letter to Commons Speaker Sir Lindsay Hoyle, protesting against having to swear allegiance to the Queen in order to take her seat at Westminster.
Mr Eastwood said: “Under protest and in order to represent my constituency, I do solemnly swear, sincerely and truly declare and affirm that I will be faithful and bear true allegiance to Her Majesty Queen Elizabeth, her heirs and successors, according to law.
“My true allegiance is to the people of Derry and the people of Ireland.”
MPs are required by law to make an oath or affirmation of allegiance to the Crown and are not allowed to speak in debates, vote or receive their salary until they do so.
On Wednesday, Ms Hanna, the new SDLP MP for Belfast South, made an affirmation before outlining her reasons for choosing to do so.
In line with the required text, she said: “I solemnly, sincerely and truly declare and affirm that I will be faithful and bear true allegiance to Her Majesty Queen Elizabeth, her heirs and successors, according to law.”
However, she added: “My allegiance is to the people of south Belfast and, in order to serve them, I’ve made this affirmation.
“My political commitment is to the Good Friday Agreement, relationships in Northern Ireland, between the north and south of Ireland, and between these islands based on mutual respect and co-operation.”
In a letter to Sir Lindsay, she added: “I submit this letter to you to register a respectful protest against the requirement that I make a statement of allegiance to the Crown as a precondition for taking my seat.
“I chose an affirmation rather than an oath, but the words do not reflect my outlook.”
After reiterating her commitment to the Good Friday Agreement, she added: “I do not believe it serves trust in Parliament for MPs to be obliged to rehearse pledges that are not true for them.”
Some SNP MPs also stressed they were making the pledge only in order to serve their constituents, with Steven Bonnar (Coatbridge Chryston & Bellshill) appearing to cross his fingers as he spoke.
His party colleague Mhairi Black said her allegiance is “first and foremost” to her Paisley and Renfrewshire South constituents as she said she was making the pledge “for the purpose of the job”.
Anne McLaughlin, also from the SNP, said her “primary allegiance is to the people of Glasgow North East and the people of Scotland”.