How should I react to an employer in the situation where they broke their written promise on stock options ?

In November, I have informed my company that I wish to take an outside offer, The new offer was giving me a stock option that could have given me a minimum of $350K and a maximum of $900K if an exit event occurred. I presented this to my present employer who gave in writing (email) that they will offer me stock options to cover for it and made a very persuasive effort for me to stay back. After a detailed analysis, I chose to remain with the present employer, who broke the promise and had not given me the stock options. They are using lies and delay tactics to procrastinate. The reasons given each time are in complete conflict of the written agreements or logic. Can I file for breach of contract or any other legal method? If yes, who should I be filing my grievance with - Attorney general of the state or Dept of Labor or someone else?