[Accyexplorer]

I'm unsure if a employer is under any legal obligation to make a employee aware of any amendments to their work contract (I'd assume they are).
But,since the foundation of any contract is that the parties involved agree to the terms,the amendment is 'nil and void' should your employer (straight away) act upon it.

If a employee is aware of a amendment but still goes to work and receives payment without voicing any concern,that could be deemed 'legally binding'.

I'd be slightly dubious of any employer who changes a employees work contract without any consultation.The fact that they did not get folk to sign this amended contract shows a degree of incompetence Imo.
Any bonafide employer should ensure,as good work practice,that this contract is understood and signed by any and all employees.
A contract gives protection to the involved parties and if not understood/signed by the parties involved,it leaves folk vulnerable in the eyes of the law.

I would talk to your employer or Rep and (in writing) voice any concerns you have with the amendments before using words like "falsifying documents" and "fraud".