Labour leader Jeremy Corbyn fears some of his supporters may have been “unfairly” barred from voting in the party’s leadership election.
He has handed a list of names to party officials, saying he wants a “fair and open” contest, with all those eligible to take part able to do so.
Allies of Mr Corbyn have claimed there is a “rigged purge” of his supporters after a union leader was excluded.
Labour said it had a “robust” validation process in place.
The Labour Party has, meanwhile, announced it has signed up a security firm to cover its annual conference in Liverpool next month, ending fears the event would have to be cancelled.