Unionists have expressed anger at a planned homecoming party for John Downey who police suspect was involved in the 1982 Hyde Park bomb.
Up to 500 people are expected to attend the event in Donegal, which has been described by some as "ghoulish".
The party is to be held at the Lagoon restaurant in the village of Termon in the north-east of the county.
A fundraising event to pay his legal fees was held at the same pub last June.
Local Sinn Fein TD Pearse Doherty said a "social event" would take place this Saturday night to "thank the hundreds of people from across the county and further afield" who helped raise funds for Downey's legal defence.
John McCafferty, speaking for the restaurant, confirmed that between 400 and 500 people were expected at the venue.
"It is good to see a bit of business, we accommodate all types," he said.
Downey, who lives in Creeslough, Co Donegal, was to face trial for the murder of four British soldiers in 1982 but an Old Bailey judge stopped the case after it was revealed that the British government had given Downey a letter, saying that he wasn't on any 'wanted' list in the UK.
However, the celebrations have been condemned by victims' groups, with Ulster Unionist MLA Danny Kinahan saying he was appalled.
Mr Kinahan was best man at Lt Anthony Daly's wedding a month before he died in the 1982 Hyde Park bombing.
"My reaction to these reports of a homecoming party is one of utter disgust," he said.
"Sinn Fein really is rubbing salt into the emotional wounds of the family and friends of those who died on that terrible day in 1982.
"This man should be on trial in a court of law, not living it up in a pub in Donegal."
Mr Kinahan claimed that the party was akin to dancing on the graves of the Hyde Park victims.
"It is in incredibly bad taste and brings shame on those who are organising the event," he added.
"I really feel these people are demonstrating the worst kind of 'who cares and so what?' attitude that is so often typical of Sinn Fein."
Victims campaigner Kenny Donaldson said: "He (Downey) will have a degree of folklore, no doubt, within the republican constituency. The victims are going to feel totally and absolutely disgusted."
Jim Allister, the leader of Traditional Unionist Voice, said: "This ghoulish celebration will sicken people across Northern Ireland and the rest of the UK.
"It is a telling reminder of the nature of Sinn Fein and their total insensitivity to victims and their unfitness for government."
* July 1998: The position of on-the-runs (OTRs) is addressed during the second phase of Good Friday Agreement negotiations. Sinn Fein claimed that as many of the cases were historic the position of OTRs was anomalous. They claimed the presence in Northern Ireland of those affected could further the peace process.
Sinn Fein is standing by its position that John Downey should never have been arrested as political outrage grew across the UK that almost 200 on-the-run republicans have been granted so-called 'get out of jail free' cards.
Stormont is teetering on the edge of collapse after the First Minister issued the Government with a 24-hour deadline following revelations that almost 200 terror suspects on the run from justice were told they would not be prosecuted if they returned home.