"Whistleblower" laws prohibit employers from retaliating against employees who turn in their employers for breaking the law.
In the U.S., the Federal government and most states have whistleblower laws. You can find cites to the state laws in the Employment Law Yearbook, Appendix 14B (Practicing Law Institute) and the National Survey of State Laws.
Environmentally-related whistleblower laws are usually enforced by the United States Department of Labor.
John T. Boese's Civil False Claims and Qui Tam Actions (Aspen Publishers) is a leading whistleblower treatise.