Hey, freelancers: Remember that Web design project that, once completed, unexpectedly became a “volunteer opportunity?” Or the business that diligently assigned ad copy work — but was MIA when it came time to pay for it? A union for independent workers has launched a Web platform for independent workers to air their grievances against their so-called “deadbeat clients.”

The “World’s Longest Invoice,” as it’s called, launched Thursday and already 1,500 people have posted an average of $5,000 of unpaid work each, adding up to an eye-popping $7.5 million in delinquent checks, said Freelancers Union director Sara Horowitz.

(Freelancer’s Union)

The projects run the gamut of freelance work, but many include some form of advertising or public relations, design, tech work and editing. Granted, none of the entries can actually be verified, and they stand little chance of getting paid simply because of an online post. But Horowitz said she hopes the site draws attention to challenges many independent workers face when it comes to collecting from their clients.

“Over the years, it’s always one of the top three problems our members have reported,” Horowitz said. “Lawmakers need to see the real-life impact that deadbeat clients are having on independent workers and entrepreneurs.”

She said 77 percent of respondents to an e-mail survey of the Union’s members said they’ve been “stiffed” at some point in their careers. The Union, which was formed in 2011 out of a nonprofit that was founded in 1996, has 170,000 members, Horowitz said.

While traditional employees can take payment complaints to the Department of Labor, freelance employees are less protected when it comes to collecting payment from clients. The group has already brought forward legislation in New York state that would allow freelancers to file complaints over missing payments with the Department of Labor. That bill has passed the Assembly, and Horowitz said she hopes the World’s Longest Invoice will give other states the same idea.

The Government Accountability Office estimates that so-called “contingent workers” comprise 31 percent of the total workforce.