JEREMY Corbyn’s chances of holding on to the top job in Labour took a hit yesterday when the party severely restricted who could vote in the leadership contest .

Tens of thousands of union members may be banned after members of the party’s ruling NEC tightened the rules.

It adds to measures announced on Monday to stop anyone who has been a member for less than six months having a vote.

As details of that original Monday meeting emerged, it seems as if the critics of Corbyn on the 33-member NEC waited until he and one of his supporters had left the room to vote on the proposals.

After that measure was made public, more than 3,000 people joined Britain’s biggest union, Unite, in a single day.

The influx of new members came after General Secretary Len McCluskey called on those who supported to Corbyn to sign up.

The only way those who have not been members of Labour can now have a vote in the leadership election is to pay £25 and become a registered supporter. And the only time to do that will be next week, between June 18 and 19.

During last year’s leadership contest, the cost to register as a supporter was £3.

After yesterday’s decision, Unite, which is the party’s biggest affiliated union, got support at its conference for a motion calling on Labour MPs to face reselection every five years.

Although it has no power, many Labour MPs will be members of Unite and receive funding and support from the union in the run-up to elections. It’s likely the union will try and have the measure adopted by the party.

Labour MP Jess Phillips, who is not a fan of Corbyn, said: “I wonder if Unite would back the same for their workers. If a worker was great at their job and liked by the people they worked for, would it be acceptable for the board of directors to make them reapply for their job because the masters and the investors didn’t like them?”

A Unite spokesman said: “This vote today simply reflects the immense frustration that our members feel.

“They look at the conduct of some within the party, the challenge to the elected leader and they feel angered.

“They want Labour fighting the Tories, not among themselves.”

The bitterness, infighting and threats of intimidation in Labour is such that half of the female shadow cabinet ministers who resigned from Corbyn’s cabinet have said they have faced threats of abuse, death and rape.

The NEC has taken the unprecedented step of suspending every local party in the country until the leadership election is over.

Meanwhile, a Labour donor is taking the party to court after the NEC voted to allow Corby’s name to go on the ballot for the leadership contest automatically. The party’s rules were ambiguous, with Corbyn’s critics saying he, like any challenger, would need to secure the support of 20 per cent of the parliamentary party.

His supporters argued that as he was the one being challenged he should be on the bill automatically.

Corbyn has struggled to lead his party in parliament, and would be unlikely to get the necessary support, which works out at around 51 MPs.

Michael Foster, a former parliamentary candidate, has instructed lawyers, saying it was “about the rule of law”.