All organisations, including charities, have to register with the commission if they spend more than £20,000 in England or £10,000 in Wales on campaigning prior to an election.
The act also imposes a collective spending limit of £390,000 on joint campaigning.
Since Theresa May called the snap election, Friends of the Earth, the Britain Yearly Meeting of the Religious Society of Friends (The Quakers), Stonewall, Arthritis Research and the League Against Cruel Sports have all signed up with the Electoral Commission.
The Electoral Commission recently confirmed in a letter to Greenpeace that it would be retrospectively applying election spending rules for the year before the 8 June election, a decision that Greenpeace has threatened to challenge in court.
The lobbying act has been heavily criticised by many charities, with both Greenpeace and Friends of the Earth calling the law "illiberal" and a "terrible piece of legislation" after the two groups were fined for failing to abide by joint campaigning rules before the 2015 general election.
The Labour Party and the SNP have both pledged in their manifestos to repeal the lobbying act.
But the Electoral Commission defended the act in a blog post for the National Council for Voluntary Organisations, claiming that the impact on charities was "exaggerated" and acknowledging that the timing of the new election would make complying with the rules difficult for some charities.
The blog said: "Those who were expecting the next general election to be in 2020 may not have anticipated six or 12 months ago to be having to assess their spending in this way now. We appreciate that, for some, this retrospective regulated period will present a challenge.
"That is why we are taking a pragmatic and proportionate approach. In particular we recognise that, as a UK general election was not due until 2020, many will not have been running campaigns that could reasonably be regarded as intended to influence people to vote in a particular way."
Some prominent figures in the charity sector, including Sir Stephen Bubb and the philanthropist Gina Miller, have called on charities to speak out more ahead of next month’s election despite the lobbying act.