Is it legal to terminate an employee while they are receiving workman's compensation in PA?

It is always lawful for employers to discharge employees, for good reason, bad reason, or no reason, as long as no statute or contract is violated.

The WC statutes do not prohibit firing WC beneficiaries - they prohibit firing employees BECAUSE they claimed WC. An employee with a bad attendance problem , or a thief, can be fired after claiming WC, just not BECAUSE of the WC claim.