Should I sign a performance improvement plan that I don’t agree with?
No, you shouldn’t – even if you are being pressurised into doing so by your employer. It is very difficult to argue against an unfair PIP or process once you have already agreed to it.
It is best to speak to your line manager or HR and try to narrow the issues, and if necessary, lodge a grievance as to why you think the PIP is unfair. It is also a good idea to take early legal advice.