A left-wing political party has accused Labour of a “witch hunt” against people signing up to back Jeremy Corbyn in its leadership contest.
Left Unity said Labour should be “thrilled” so many people want to join rather than focusing on “people who it thinks are too left wing”.
It comes after The Times reported “infiltration” of the contest to replace Ed Miliband by the “hard left”.
Labour says it has a “robust system” to prevent “malicious applications”.
Ballot papers have not yet been sent out in the leadership contest, which pits Mr Corbyn against Yvette Cooper, Liz Kendall and Andy Burnham.
Labour says the verification process is ongoing, and has refuted claims the leadership contest is being infiltrated by those who do not support the party.
Acting leader Harriet Harman emailed MPs this week with a list of new members from their constituencies, asking them to check for any suspicious names.
As well as regular members, people can sign up as registered supporters for £3 and take part in the vote. They are asked to confirm they “support the aims and values of the Labour Party”.
The Times reported 18 members of Left Unity, a left-wing party founded by film director Ken Loach which fielded 10 candidates at the general election, had registered.