Electors in an area of Bognor Regis will be going to the polls next month.
The way they cast their vote in Orchard ward will determine the political balance of the town council.
A win for the Conservatives will see them take overall control of the town council. If the Liberal Democrats keep the seat, it will stay a hung council.
Polling day is on June 14. A full list of candidates will be published by May 18.
The by-election has been caused by the resignation of Lib Dem Peter Lee.
He was elected last May in results which gave the Tories eight seats on the 16-strong town council, the Lib Dems six seats and one each for Labour and the Independents.