My boss had informed me that I must sign a legal document indicating that I will not work for any other private company in the same field (i.e. a competitor) for three years after my date of termination from our company. Can I be forced to sign this? All employees are being threatened with job termination if we do not sign the non-competition forms.

The employer can make signing it a condition of continued employment. Whether that particular restriction would be enforceable or not, however, is really best answered by a local attorney. Different states have very different stances on what is considered "reasonable" in a noncompete and what is considered "unreasonable". Could also depend on the type of work you do.

Can they withhold my next paycheck for not signing the non-compete document? I have already been instructed that if I do not sign the form, I will be terminated, however, they are also threatening to not give me my next paycheck until I turn in the signed form. Is that legal?

No, that's never legal.

No, they cannot hold your paycheck.

Thanks, you have been very helpful. One last question: what if there are multiple typos in this document? Does it void the specific sentences that contain the typos? Some of the sentences don't make sense due to spelling errors.

If your forced to sign it or you will be fired, tell them to include that language in the document. They wont a contract signed under deres is seldom enforceable. The problem is they can fire you for not signing it. Contact an attorney to see if it enforceable before you sign.
JoeC