Labour supporters who prefer not to join the party will be able to help pick its 2016 Mayoral candidate in return for paying a £3 fee.
The party will select a candidate via a Primary – a ballot in which party members and non-members who register as supporters will be able to cast a vote.
It was recently reported that the party could charge as much as £10 to take part, a price several potential candidates warned risked pricing out many supporters.
David Lammy, the only MP to so far declare he’s seeking the nomination, launched a petition calling for the fee to be capped at £3.
At the time he said: “When Londoners are struggling with rocketing rents, soaring energy costs and stagnant wages, we cannot ask people to cough up £10 to vote and seriously expect many to do so.
“Such a high fee would be counter to the very aims of a primary and will do more to turn people off the process entirely than draw them in.”
His concerns were echoed by Christian Wolmar, the only other declared candidate, as well as possible contenders Diane Abbott and Dame Tessa Jowell.
Writing in the Evening Standard, Dame Tessa said: “Clearly the money raised should be sufficient to cover the administrative costs and ensure the integrity of the process, but this should not be so expensive that the very people we seek to involve are deterred by the cost of taking part.”
On Tuesday evening the party confirmed supporters would be asked to pay £3 to select a candidate to succeed Boris Johnson when he steps down in 2016.
Mr Johnson was himself selected by a primary in 2007 in which non-Conservative members paid £1 via their phone bill to take part.
Labour will be hoping their ballot attracts more than the 20,019 members and non-members who voted in the Tory selection.
Speaking on Wednesday, Mr Lammy said: “I’m very pleased that the NEC has recognised the need for the London primary to be as accessible to Londoners as possible.
“The primary offers a unique opportunity to engage with new voters on a wider scale than ever before and a low fee is crucial to enable that to happen.
“I would ideally have liked to see a £1 fee to allow as many Londoners as possible to get involved in choosing the Labour candidate for Mayor, but clearly £3 is a huge improvement on the £10 fee originally mooted.”