Belfast's Sinn Fein Lord Mayor Deirdre Hargey will be urged to make a statement directly to the police about the murder of Robert McCartney in an unprecedented council motion next week.
The DUP and SDLP motion will call on her to tell the PSNI what she saw in Magennis's bar on the night the father-of-two was stabbed to death.
It will also ask Ms Hargey to agree to the McCartney family's request - made three months ago - to meet them.
The family last night said they were dismayed that the Lord Mayor was attending events at which she championed human rights but "never once had the decency to contact us in the 13 years since our brother was murdered".
The McCartney sisters will be in the public gallery for Monday night's council meeting.
No previous Lord Mayor has faced such a motion and it is set to cause considerable embarrassment in the corridors of City Hall.
DUP council group leader Lee Reynolds said: "We have spent the summer months with the McCartney family working on the next step forward in their campaign for justice.
"Part of that is bringing this motion forward to council and we welcome the SDLP seconding it."
Robert McCartney was stabbed to death by IRA members outside Magennis's bar in January 2005. Ms Hargey was one of 70 people in the bar that night who said she saw nothing of the fight in the premises that ultimately spilled outside and ended in murder.
Robert McCartney's sister Catherine told the Belfast Telegraph: "That is simply not good enough, especially for someone who is now the first citizen of this city.
"This is not a historic case where the people involved are dead and it's hard to obtain information.
"Except for Jock Davison, everybody central to events on the night Robert was murdered is alive. Deirdre Hargey needs to go to the police and make and sign a statement.
"This is 2018. There is no reason whatsoever for her not doing so. She would be setting an example to the other Sinn Fein members in the bar that night.
"We have been told of the 20 present none made a statement directly to police."
By making a statement to the PSNI, Ms Hargey would be demonstrating to "non-republicans in Magennis's that night that it is okay to talk to police and they have no reason to be afraid of coming forward", Ms McCartney said.
The Lord Mayor has said she was never asked to make a statement to detectives.
Ms McCartney said: "I will be meeting police to ask them why that was. But Deirdre shouldn't need to be asked, she should have automatically volunteered to go herself.
"She also should have contacted our family long ago. Deirdre has been attending a range of meetings since she became Lord Mayor and voicing her support for ensuring people get human rights and justice.
"In our opinion, she needs to start delivering on the principles she claims to espouse.
"My brother was an innocent man who went for a drink in a bar and was murdered. Surely any political representative in the bar that night should be bending over backwards to help the victims' family in any way possible."
Ms McCartney said her family wanted to sit down with Ms Hargey "and ask her what exactly she saw and didn't see that night - where she sat, if she saw Robert, if she saw Jock Davison".
On becoming Lord Mayor in June, Ms Hargey insisted she had done all she could to help the McCartneys get justice.
She said she had "fully complied" with the police investigation. The PSNI had not asked to interview her but she would be willing to talk to detectives if requested, she added.
Ms Hargey said: "I want to take this opportunity to again extend my sincere condolences to the McCartney family.
"What happened to their brother Robert was wrong, it should not have happened.
"I complied fully with the investigation and I'm conscious that there is an ongoing investigation that is still live into this case. But the family do deserve justice.
"My main concern is to ensure the family receives justice and I feel that needs to be done through the PSNI. I do feel that any information around incidents pertaining to that night needs to be done through those avenues and I would be open to doing that, as I have done in the past."
The Lord Mayor insisted the murder would not overshadow her term of office. But Ms McCartney said: "Robert's image will be hanging over Deirdre Hargey for the entire time."
Ms Hargey was dropped as a prospective Sinn Fein election candidate and temporarily suspended from the party in 2005 after it emerged she was in the pub on the night the fight erupted. With CCTV video tapes removed from the bar in the wake of the killing, and widespread reports of witness intimidation, the IRA was accused of a cover-up.
The council motion calls on "the Lord Mayor to urge her party colleagues and all those present in Magennis's bar that evening to come forward to the PSNI".
It also urges the Police Ombudsman to publish its report into the McCartney murder "without further delay".