UUP leader Robin Swann has called for a unity candidate to run in the West Tyrone by-election to send a message that "the disrespect shown to victims of terrorism will not be tolerated".
Former Sinn Fein MP Barry McElduff resigned the seat in January after appearing to mock the victims of the Kingsmill massacre in a video he posted to Twitter in which he placed a loaf of Kingsmill bread on his head.
In a statement on Sunday, Mr Swann said he was repeating his call for a non-partisan candidate initially made in the aftermath of Mr McElduff's resignation.
"It is clear that Sinn Fein has learnt nothing from the appalling disrespect shown by Barry McElduff. Only last week they failed to condemn the banner put on display in Newry describing one of the IRA’s most ruthless terrorists caught in possession of one of the murder weapons used at Kingsmills ‘our hero’," he said.
"Given that McElduff resigned over his own insult directed at the Kingsmills’ victims, it is appalling that Sinn Fein can sit and acquiesce whilst yet another insult is put on visual display in Newry."
There was anger from the unionist community earlier this week after a decision to erect a banner dedicated to IRA man Raymond McCreesh at the controversial park in Newry which bears his name.
McCreesh, from Camlough in Armagh, was reportedly in possession of a rifle used in the 1976 Kingsmill Massacre killings when he was captured later that year.
"It seems that nothing has changed in terms of Sinn Fein’s attitude towards victims of terrorism and for that reason I will continue to do what I can to facilitate a voice for victims in the forthcoming by-election and I thank those who have been doing what they can as well," Mr Swann added.
"However, time is short with nominations closing on 10th April. If it cannot be achieved, we will have to consider other options."
Sinn Fein announced in February it had selected 26-year-old Orfhlaith Begley to contest the West Tyrone by-election.
The Alliance Party previously declined to support a victims candidate, announcing Stephen Donnelly would contest the seat and it is understood SDLP MLA Daniel McCrossan, who finished third in the 2017 election, will contest the seat for his party.