Cite your sources and resign before taking legal action if your contract is breached by the employer.
April 15, 2012
Terry Bossname
Company Name
Company Address
Dear Mr./Ms. Bossname
It has come to my attention that (company name) is in breach of contract with me as an employee by (cutting my hours, posting my job without consultation, refusing a review session, etc.) I have addressed my concerns with (name) and (name) and since no action has been taken to correct the problem, I find it necessary to resign and sue for financial damages and breach of contract.
Specifically, Section (number) of the contract is in violation in that (description of violation.) I have taken the following steps to address it: (steps.) All of my efforts have been ignored. My resignation is effective immediately, and I shall be in contact to discuss the terms of damages and compensation.
Sincerely,
Your Name