The by-election to replace killed Labour MP Jo Cox is expected to take place on 20 October.
The Conservatives, Ukip, and the Liberal Democrats have said they will not stand a candidate at the Batley and Spen by-election as a mark of respect for the former MP.
Labour has opened the selection its candidate; the deadline for applications is on Friday 16 September.
A hustings event to choose between the party’s applicants will take place on 23 September.
Right-wing groups, Liberty GB and the English Democrats, have both said they will contest Ms Cox’s former seat despite the major parties standing down.
Labour is widely expected to win the seat, which it has held since 1997.
Ms Cox was shot and stabbed by an attacker in Birstall, West Yorkshire on 16 June, during the European Union referendum campaign.
Thomas Mair, 52, was charged with murder in relation to the MP’s death and is set to go on trial in November of this year.
