Alex Cunningham, the MP for Stockton North, said the party had already removed around 1,200 people who had no right to vote.
Labour MPs Simon Danczuk, John Mann, Graham Stringer and Barry Sheerman have all criticised the voting process and called for it to be halted.
They claim non-Labour supporters are infiltrating the vote to ensure that left winger Jeremy Corbyn is elected.
A poll yesterday showed that he had enough support to win the race without second preferences being taken into account.
Mr Cunningham admitted to Premier that there was "a lot of mischief going on" but rejected calls to halt the vote.
"There is a robust process in place and I'm hopeful that we will catch those who don't really have the interests of the Labour Party at heart," he said.
He added: "I don't think we should halt it at all. There's some 1,200 people who've been rooted out so far who have no right to be in the Labour Party.
"I think we've seen some disloyalty amongst other politicians who claim that they now support Labour when we know that's not the case."
Labour said the people excluded from the vote included 214 from the Green Party, 37 from the Trade Unionist and Socialist Coalition, 13 Tories, seven from Ukip and one from the BNP.
The process of stopping bogus supporters from influencing the contest, the result of which will be announced on September 12, would continue once the deadline passed, the party added.