Filing a labor complaint when forced to sign on demotion

Hi.

I have been promoted from Coordinator role to Manager role in February 2017. In these months I have never received any complaint from my manager regarding my performance, no any written notice or warning.

A month ago, my manager said that she thinks I have some communication problem, and I cannot work under stress. For that reason, my manager wants to demote me and cut my salary. It has been said in the email without any clarification.

Next day, she called me for a meeting to offer me Support position and said that my salary will be decreased by 35%. I agreed verbally, as I have been scared to lose the job if I do not take this offer.

There hasn't been any notification in writing provided to me. Now, I have to renew my visa as my company will cancel my old visa to apply for a new one, and I will be requested to sign the letter with the demotion. I don't want to do this, as I think it is illegal.

May you please advise what will happen if I refuse to sign that paper and if they will terminate me because of it.

Thanks.

Tatiana.