Employment / Labor Attorney
You are probably going to be very hard pressed to find an employment attorney that does work pro bono as these tend to be extremely intricate cases that can take several years to develop. Moreover, employment cases are high risk in that there is certainly no guarantee of success.
That said, most employment attorneys work on what is called a contingency fee basis, which means that they will only get paid, if you get paid. Most employment attorneys will also do free consultations to discuss your case. Good luck.
This answer is solely for assistance via the AVVO network. My answer to this question does not create an attorney-client relationship.