Councillors are set to meet in Hove Town Hall next Tuesday (March 5) to decide which party will take control of the local authority.
This comes after a Labour councillor crossed the floor and joined the Conservative Party last week.
The council, which is currently run by Labour under a minority administration, could be taken over by the Conservatives just months before the local elections in May.
But it is the Green Group which will hold the balance of power in the vote on Tuesday.
The Conservatives now have 21 councillors to Labour’s 19, but two members under newly-formed The Independent Group (TIG) said they would vote with their former party Labour.
This means the 11 Green councillors could decide the fate of the local authority – or abstain.
If they were to abstain and there is a deadlock, the mayor has the casting vote – and that position is currently held by Conservative councillor Dee Simson.
The move comes after Cllr Anne Meadows switched from Labour to the Conservatives last week.
And since then another Labour councillor – former council leader Warren Morgan – has left the party to form a new group, The Independent Group (TIG), with former Labour colleague Cllr Michael Inkpin-Leissner.
Brighton and Hove City Council said: “The current political leadership arrangements continue for now. Under our constitution, any change in leadership can only take effect following a decision at a meeting of the Full Council when all currently elected councillors agree who forms the administration and who is voted to be Leader of the Council. Councillors decide whether and at which meeting the business is discussed.
“Subject to the will of councillors, the day to day operation of services to the public will remain unchanged in the short term. Council officers will continue to use their delegated powers to ensure a consistent service.”
The Extraordinary Meeting, of the Council has been called for Tuesday, March 5 from 4.30pm at Hove Town Hall.