New York City, NY

A few weeks ago I quit my full-time job. The same company I was working
for now wants to hire me as a freelancer. However they say it is against
labor laws to hire me until I have not worked there for 6 months. They say
that the only way they can legally hire me is to have me go through a
freelance agency. Is this a real labor law??

No, it isn't. But if they want you to go through an agency they can require it.