Can you be forced to sign a contract?

In theory, no - it contravenes your rights under employment or contract law in most western countries. In practice, the consequences of not signing (or agreeing to the terms of) a new contract can be expensive or even result in loss of employment, and while due process may be pursued in the courts, it often seems easier simply to acquiesce, and to sign a contract against your better judgement.

If you feel that you are being forced to sign a contract against your will, you should reference local law on the subject. If you are a member of a union, it would be best to discuss your options with your union representative before signing a new contract of employment.