A Castlereagh councillor has resigned from the DUP after being a party member for 23 years.
Ian Paisley and Martin McGuinness have been getting along well
Charlie Tosh is the latest DUP member to leave the party since it entered power-sharing with Sinn Fein.
Mr Tosh said a disagreement with another DUP councillor had been the last straw.
However, he also said he was disappointed by pictures of First Minister Ian Paisley laughing with Sinn Fein's Martin McGuinness.
"I think that when one considers the atrocities that have been commited in Northern Ireland, I find myself in complete agreement with Jim Allister, that to see the 'chuckle brothers' together in government makes me ill," he said.
Following the announcement, Mr Allister said Mr Tosh's decision reflected the "unabated unease within unionism over DUP/Sinn Fein government".
"Like many traditional unionists he has reached the measured conclusion that he cannot be a party to unrepentant terrorists in government," he said.
"He will not be the last DUP public representative to take this honourable course."