An under-pressure Sinn Féin MP is set for a meeting with party leaders to explain an online video showing him with a Kingsmill-branded loaf on his head on the anniversary of the Kingsmill massacre.
Barry McElduff has been summoned to meet the Sinn Féin leadership tomorrow.
The furore around the West Tyrone MP's social media post is threatening to further disrupt faltering efforts to re-establish a powersharing executive at Stormont, with the Democratic Unionists characterising it as an affront to victims.
Mr McElduff has apologised for Friday's post, insisting it was not meant as a reference to the republican murders of 10 Protestant workmen in 1976.
He has offered to meet relatives of the sectarian outrage but a number of them, including the only survivor of the gun attack, Alan Black, have rejected the invitation outright.
This evening a Sinn Féin spokesman said: "The party leadership will be meeting with Barry McElduff tomorrow."
The Police Service of Northern Ireland is examining the video after receiving a number of complaints, while the Parliamentary Commissioner for Standards at Westminster has also been alerted.
The well-known Kingsmill brand of bread shares a name with the south Armagh village that witnessed one of the most notorious incidents of the Troubles, when gunmen stopped a van carrying textile workers on their way home, identified the Protestant occupants, lined them up at the side of the road and shot them.
In the short video, Mr McElduff, who is known for his light-hearted social media contributions, is filmed walking around a shop with a Kingsmill loaf on his head, asking where the store kept the bread.
It was posted on the 42nd anniversary of the Kingsmill outrage.
He has faced multiple calls to resign in the wake of the controversy.
Condemning the video, DUP MP Emma Little Pengelly referred to Sinn Féin's oft-repeated phrase during the powersharing crisis, that it will only return to Stormont if the institutions operated on the basis of respect, honesty and integrity.
"This is a test of the Sinn Féin leadership's commitment to 'respect, honesty and integrity'," she said.
"The party's West Tyrone MP posted a grossly offensive video. People across these islands have condemned the video mocking the Kingsmill massacre. He should hang his head in shame."
Mrs Little Pengelly accused senior Sinn Féin party figures of going silent on an issue she said had sparked "incredible outrage throughout the community".
"Regardless of what explanation Barry McElduff offers, the facts are uncompromising," she added.
"Of all the products in the shop, and of all the brands of bread in the shop it's very bizarre why Mr McElduff chose Kingsmill.
"Indeed, even stranger as to why he chose to do this on the 42nd anniversary of that barbaric act when ten innocent men were shot because they were Protestant.
"The Sinn Féin leadership must condemn this crass action."
On Saturday, the republican MP deleted the video and apologised.
"When I posted the video I had not realised or imagined for a second that there was any possible link between the brand name of the bread and the Kingsmill anniversary," he said.
"It was never my intention to hurt or cause offence to anyone and in particular to victims of the conflict who have suffered so grievously.
"I apologise unreservedly for the hurt and pain this post has caused."
Mr Black, who survived the gun attack despite being shot 18 times, rejected Mr McElduff's apology.
"It was like a punch to the stomach, it was so callous," he told the BBC.
"To mock the dead and dance on their graves is depraved.
"It was designed, in my mind, it was designed to cause maximum hurt and it's done its job in spades."