"And the thing that really upset me about that meeting was that the Labour Party leader voted against the proposal to have a secret ballot to protect colleagues", she said.
However, there was also a setback for Mr Corbyn as the NEC changed some rules for the contest, so people can only vote if they have been a member for at least six months.
This afternoon Unite issued a threatening message to the 172 MPs who backed a no confidence vote against Mr Corbyn last month, telling them being in Parliament was not a "job for life".
"I'm in this contest to win it and that's what I intend to do".
Following Tuesday's decision, the NEC has faced criticism from supporters of Jeremy Corbyn's leadership who accused the committee of allowing the post-Brexit Labour sign ups to do so under false pretences - the assumption being that they would be able to vote for the leadership.
Labour's ruling body has blocked new union members from voting in its leadership election unless they pay £25.
In a statement, Corbyn said the incident was "extremely concerning" and that he had also been subjected to threats. If Corbyn, who was elected last September and retains strong support among the party's more left-leaning rank-and-file members, is re-elected in the contest, the party may split.
He will join fellow MP Angela Eagle in trying to wrest the party leadership.
Almost 130,000 people have joined the party since the European Union referendum.
"I thought at the time the tradition of the Labour Party and the tradition of left-wing engagement to remove dictators was a noble, valuable tradition, and one that in South Wales, from the Spanish Civil War onwards, we have recognised and played a part in".
Foster, who said he did not vote for Corbyn, denied that "this is about politics" saying: "The advice that was taken was not given the expert consideration that it would receive from a High Court judge, and everyone in the [NEC] room had a different political agenda".
Cathryn Mills, 45, a charity worker from Manchester, said she has always supported Labour but joined the party two weeks ago specifically to support Jeremy Corbyn.
Most Labour MPs have deserted the left-wing leader but he remains confident of grassroots membership support.
"These are people working in Jeremy's name, they are people around Jeremy", she told Today.
The timetable for the contest will be published on Thursday but reports suggest it will run well into September.