Pressure has mounted on the Ulster Unionists to withdraw another of their Conservative-backed election candidates after Orange men made a direct plea to the party to stand aside.
Loyal orders in the marginal South Belfast constituency have written an open letter to UUP leader Sir Reg Empey calling on him to strike a deal with the Democratic Unionists that would see both parties backing a pro-union independent in a bid to wrest the seat from the nationalist SDLP.
The signatories from the Orange and Black institutions in the Sandy Row area also warned that they would be instructing their members not to vote for any party that stood in the way of a so-called unionist unity candidate.
The demand comes after a similar agreement was sealed in Fermanagh and South Tyrone that resulted in the DUP and UUP stepping aside in favour of a non-affiliated candidate taking on the sitting Sinn Fein MP.
"If you can do a deal in Fermanagh and South Tyrone, what possible excuse can there be for not doing so in South Belfast?" the letter challenged Sir Reg.
The intervention will place further strain on David Cameron's electoral partnership with the UUP in Northern Ireland.
The UUP/DUP pact in Fermanagh sunk a pre-campaign pledge from Mr Cameron that an Ulster Conservatives and Unionists New Force (UCUNF) candidate would stand in all of region's 18 constituencies.
But defending the party's decision to support the arrangement in Fermanagh, senior Tories insisted it was a one-off and were adamant there would be no repeat in South Belfast.
Shadow secretary of state Owen Patterson said: "There is no desire to have any such arrangement elsewhere."
However, the Sandy Row loyal orders urged Sir Reg to sign up to another localised pact, even though both the DUP and UUP have already nominated candidates.