The crowdfunding page has been live since 7am on Sunday, yet more than £20,000 has already been raised.
The challenge is being brought by Ciaran McClean on the grounds that the political pact is in breach of the Good Friday Agreement and Bribery Act.
McClean, who is a Green Party member in Northern Ireland, said that the Tories are jeopardising the peace agreement by aligning themselves with the DUP.
The DUP agreed to support May’s minority Conservative government in key Commons votes in return for an extra £1 billion more funding for hospitals, schools and roads in Northern Ireland.
McClean has launched the fundraising page in order to help pay for his legal costs in bringing this challenge about.
McClean said: “I have spent most of my life campaigning for peace in Northern Ireland.
“The deal concluded between the government and the DUP threatens everything we’ve worked so hard for and I’m bringing this case to ensure the government is held to account.”
He is being represented by solicitor David Greene, partner at Edwin Coe solicitors, who represented hairdresser, Deir Tozetti Dos Santos, one of the successful lead claimants in the Brexit Article 50 challenge up to the Supreme Court.
Greene said: “This case is of huge public importance and demonstrates that individuals can call Governments to account and the importance of that capability in a democracy.”
Writing on the Crowdfunding page, McClean adds: “My claim is that as a citizen I expect my Government to honour its obligations under the Good Friday Agreement and not to bribe others with money so that it can stay in power.
“My lawyers have put these points to the Government. They eventually responded failing to meet deadlines they set themselves. Nothing they said addresses the fundamental issues behind this corrupt deal.”
Joanna Sidhu, a former litigation lawyer at CrowdJustice, told HuffPost UK on Sunday: “CrowdJustice has seen a flood of donations supporting this potentially game-changing legal challenge since the campaign went live this morning, showing how powerful a community can be when given the opportunity to come together.”
Sidhu added: “Having campaigned for peace in Northern Ireland for most of his life, Ciaran McClean is bringing this legal challenge to hold the government to account.
“By launching a crowdfunding campaign to support this challenge, Ciaran is giving everyone the opportunity to be part of the fight to preserve our democratic values.”