Momentum, the pro-Jeremy Corbyn pressure group, has seen thousands of new members join the organisation since the general election, it emerged on Wednesday 28 June.
A Momentum source told IBTimes UK that the group, founded by Jon Lansman as an offshoot from Corbyn's successful Labour leadership bid in 2015, now has 27,000 members, up from the last reported figure of 22,000 before the 8 June vote.
The organisation said it would continue to use viral social media content and new organising techniques to target voters across the UK.
Momentum, among other things, is planning to roll out an "extensive" training programme in new marginal constituencies in a bid to boost community organising for Labour in those battleground seats.
National organiser Emma Rees said the group, despite its relatively small operation out of the headquarters of the transport union TSSA by Euston Station, London, thrived on ambition.
"During the last election we operated on a limited budget, punched well above our weight and helped swing key seats for Labour," she said.
"With Theresa May leading an unstable, minority Conservative government propped up by the anti-abortion, anti-gay rights, climate change-denying DUP, another election could come at any moment."
Rees added: "This is why we're launching our campaign now. We must stay on the front foot, and prepare for a possible snap election.
"The Conservatives will learn from their disastrous campaign, and won't make the same mistakes twice. In response, Momentum will ramp up its operation and help build a network of first time canvassers and door knockers the likes of which Britain has never seen before."
The news comes as Corbyn and Labour enjoy a post-election opinion poll surge as May clings onto power. The latest opinion poll from Panelbase, of more than 5,400 voters between 16 and 21 June, gave Labour a five point lead over the Conservatives (46% versus 41%).
Labour, with 30 extra seats, is also experiencing a period of unprecedented unity under Corbyn, who faced a vote of no confidence from the Labour parliamentary party and a failed leadership challenge from Owen Smith MP in 2016. But the UK's split from the EU risks creating divisions within Labour.
The party's manifesto said Labour accepts free movement of EU nationals to the UK would have to stop after the split.
However, some Labour MP want to maintain a close relationship with the EU and maintain extensive access to its single market, which could require the UK accepting some elements of free movement. Momentum, with its young supporters, has been a staunch defender of the EU's free movement of people rules.