I've been with the employer about 2 and 1/2 years. I am working remotely and have been in the office 2 or 3 times to meet coworkers. They are asking us to sign a policy now and acknowledge amongst other things they have the right to update or change this policy at any time including asking
employees to report back into a physical office location at any time, for any reason, where
allowed by law. If we don't sign by a specific date, they are threatening repercussions but nothing specific. What should I do?

I am sorry to hear that you have been put into this situation. It is always rough when your employer is attempting to force changes with threats.

You should contact us. You should not sign anything before having a lawyer review your employment contract and the documents they are now pressuring you to sign. If the company is asking you to sign something, they are attempting to change a core part of your employment. The company may be attempting to change other parts of your employment, such as vastly limiting your termination entitlements. These are things the lawyer can flag.

Unfortunately, this would come down to the specific wording of your employment contract, the new policy, and any other relevant documents. The inclusion of a single word in a clause can completely invalidate it and have a dramatic impact on your rights and entitlements. Due to this, you will likely have to pay a lawyer to review your documents. However, this would be money well spent to make sure you are on solid ground as to your rights, and cannot be forced into the office full-time.