You're probably SOL with the regional in question, but there are many others who will hire you with ATP mins and a pulse...literally. Of course they may not be the best places to work.

Pilots aspiring to airline careers are far more exposed to to the whims of previous employers than a normal job applicant. Keep that in mind and avoid any friction with future employers and bosses...if you don't like an employment situation, resign professionally giving at least two weeks written notice (or more if the company policy requires it).

You could discuss this with a lawyer, depending on the circumstances you might have a case against the former employer but on the other hand it's probably not a good idea for an aspiring airline pilot to have a public record of suing past employers. Lawsuits are public record forever, and many or most high-end employers will search for those.