The Excluded Unity Alliance said Wednesday's event has attracted a cross-party line up of MPs and business people who are calling on the Chancellor Rishi Sunak to address gaps in support schemes.
The Treasury said it has created one of the largest and most comprehensive Covid-19 support packages in the world, which has protected millions of jobs and the incomes of millions more.
However, campaigners estimate that three million people have fallen between the cracks and received no meaningful support during the pandemic.
“This is an issue that strikes at the chords of my heart” said Ali Traversoni, who acts as a spokesman for the alliance.
“There is no reason why adequate and fair financial levelling up cannot be made at this stage. Not to do so is as cruel as it is baffling when others have had the support they needed."
Martin Wood, a campaigner for those excluded from Government support, added: “The excluded people are all UK taxpayers, they have all contributed into the tax system like everyone else who has been looked after - so where is their support?”
“This issue simply should not be open for debate when lives and livelihoods are at risk."
The group is due to meet outside Parliament on Wednesday June 30 to hear from a range of speakers who support people who have been excluded from support during the pandemic.
One of the speakers, Torrin Wilkins, Director of the Centre Think Tank, said saving a small business today will help to save an economy tomorrow.
He added: "I will be speaking about the importance of small businesses in the supply chain of large businesses . I agree with the Conservatives on (the need for) free markets and competition which is exactly why they need to support the excluded."
A Treasury spokesperson said: "Throughout this crisis our priority has been to protect lives and livelihoods. Our schemes have supported millions of jobs and the incomes of millions more.
“While we acknowledge it has not been possible to support everyone in the way they might want our schemes were designed to target support at those who need it most, while protecting public money against error, fraud and abuse.”
The spokesman added: "More people have become eligible for employment support schemes.
"The Government has moved the cut-off date on which employees need to be with their employer to be eligible for the Coronavirus Job Retention Scheme. For claims starting on 1 May 2021, the cut-off date has been moved from 30 October 2020 to 2 March 2021.
"This means that those employed on 2 March 2021 are now eligible for CJRS if the other eligibility criteria are met. The Self-Employment Income Support Scheme grant has been extended and is now based on 2019-20 tax returns. This has brought more self-employed people into the scope of the scheme, including many new to self-employment in 2019-20.
"Throughout this crisis, we have done all we can to support jobs and livelihoods through our £400 billion package of support, and our self-employed and furlough schemes are among the most generous in the world."