Your company underpays you. You tell them your not coming back to work until they fix it. They fire you for it. Can you sue?

By underpaid, you could only mean that the employer is improperly calculating your hours of work or is withholding from proper gross pay without your written permission.

You are foolish to not come to work as scheduled; that is a firing offense.

Not suit necessary. Complain to the nearest USDOL wage & Hour Division office. It will investigate whether pay was properly calculated and get you any underpayment due.