Was I wrongfully terminated?

Is Florida an "At will" state? I was hired in March of 2004 and upon being hired i had disclosed a prior felony on my application and verbally discussed it with my hiring manager. I was hired and received a promotion in Dec. of 2004. When I was hired as far as I know the company did not have a background check policy on the books. A few months before my termination my manager warned me that the company was going to implement a background check policy that may also have included a credit check that I never authorized or was presented with. I was terminated in Oct. of 2005 and the reason I was given was roughly ,"background check info.". Do I have a case or any recourse if the company changed their policy and in essence fired me for something that I disclosed in writing and verbally upon being hired?