Really? Can you point to a death penalty being applied for such a case? I'm not saying your wrong, but its the first I've heard of such thing. I have seen cases where the PRC has protected the rights of workers to form unions. Of course, these unions are through the government.
There's a de facto death penalty for being sufficiently troublesome. I'm not sure whether a do-not-try-to-start-an-independent-labor-union law is actually on the books or not.