More than 600,000 people are set to choose the next Labour leader, amid warnings of legal action should the party not pause the contest.
Labour said the possible total electorate for the leadership election is 610,753 after the deadline for registering to vote passed.
But the party insisted action will continue to verify those signed up and remove people who are not entitled to a vote.
Figures released by Labour show there are currently 299,755 members, 189,703 people from bodies affiliated to the party and 121,295 people who have paid £3 to register as a supporter in order to have their say.
As the deadline approached, Graham Stringer joined three other Labour MPs in calling for the race to be halted while the party attempts to weed out bogus anti-Labour voters who have signed up as registered supporters.
The surprise emergence of Jeremy Corbyn as the apparent frontrunner in the race has led to calls for it to be re-run over allegations that it has been exploited by hard-left groups and political opponents including Conservative activists.
But Mr Corbyn - who is the bookies' favourite ahead of rivals Andy Burnham, Yvette Cooper and Liz Kendall - said the public response to the leadership contest was proof of optimism that a popular, modern Labour Party could defeat the Tories.
Labour said it has already excluded 1,200 members or supporters of another party.
But Mr Stringer said legal action could be taken against the party unless it pauses the process, joining colleagues Barry Sheerman, John Mann and Simon Danczuk.
The GMB union said the total number of its members recorded with the Labour Party as affiliated supporters was 23,840.
No other union has given details of how many of their members have registered to vote.
It came as all three of Mr Corbyn's rivals called for quicker access to information about the latest raft of people who have been signing up to vote.
In a letter to Labour Party chiefs, it is understood they have raised concerns that the information has not been made available to them despite being ready to send to the printers to prepare ballot papers.
Speaking on LBC's Shelagh Fogarty, Mr Stringer said: "I think if the election isn't paused that would be a shame and I think probably that people will take legal action because the rules are not being implemented properly.
"People who basically have lied when they say they are Labour Party supporters are going to vote in the election, there's lots of credible evidence out there.
"So I think the Labour Party will end up in the chaos of legal process so I don't think it will go ahead on that basis and it's whether the NEC (national executive committee) take that decision or whether it is stopped by legal action."
Mr Mann claimed Labour's new voting system could lead to the party becoming an "unrepresentative clique" as more Londoners could have registered to vote than in other parts of the country.
But Mr Corbyn defended the "robust" system, adding: "All of our focus must be on channelling this extraordinary movement towards a united party that is able to find its confidence and defeat the Conservatives in 2020."