The charter laid out a series of commitments for businesses to follow so freelancers are treated fairly.
These include creating set payment times, setting out clear terms of ownership of intellectual property, and training finance staff and hiring managers on best practice interactions with freelancers.
Life as a freelancer:
The charter also demands transparent contract terms for freelance work, and setting clear terms regarding cancellations and deposits.
UK trade union Community, journalism training network Women in Journalism and payments network Banked are among those to have shown support for the initiative so far.
Wedding industry community What About Weddings and the UK Business Angels Association have also signed the charter.
Tamryn Settle, co-founder of What About Weddings, said the charter would go some way to making sure freelancers were treated the same as full time employees.
Speaking to HR magazine, she said: “The wedding industry is filled with amazing freelancers and self-employed people, who are far too often not treated with the same rights as full-time employees or people working in other sectors.
"We support the Freelance Charter to help give people creating and working within the wedding sector a voice, and ensure they are treated with parity of fairness.”
UnderPinned CEO Albert Azis-Clauson said the charter would be good for businesses and workers.
He said: "Many companies are failing to meet the right standards for the freelance staff they are coming to depend on.
We’re launching a charter to change that, by inviting companies to voluntarily sign up to a transparent code of conduct that will show freelancers that they’re serious about operating a genuinely fair workplace.
"This is good for the freelancers, but it’s good for companies too, who otherwise risk missing out on the value and talent of the ever-growing army of freelancers."