Trying to Make It Right

I quit my job two days ago, due to stress, faulty equipment, nepotism,
favoritism, theft and discrimination. I was employed by an outsourcing firm
for a corporate client. I would like to send a letter to my former
employer's corporate headquarters, and also to the state, to discuss what is going on at this worksite. I am unsure of
what state agency I should send it to, or if I can at all. Any advice you
give would be greatly appreciated.

It depends what you are reporting but the Department of Labor and/or attorney general are both good places to start.