Begin looking for work. Thomas has articulated this well on HN in several places, including here:

https://news.ycombinator.com/item?id=14705531

It is hard to remain cool headed and rational about it. But at least try, or get a third person to give you some candid feedback.

If the PIP is merely a form of being soft-fired, then give it a token effort and seriously look for a new job.

If there really is room for improvement on your part in some specific area, then why not work to the program and see if you can make an improvement? I would still start looking for new work as a plan B.

If you want to keep the job, follow the plan.

I had a client who was put on a plan and they hoped he would quit. He was irked but he stayed. The manager eventually quit.

It really depends on the manager and the org. I've seen two or three folks put on a pip, strive to do better, and stay, becoming great contributors. I've also seen cases where they were set up to fail and the pip was just a cya for the org to justify the firing. It usually leans towards a firing or a "managing out."

Document and record anythi that could be relevant to future lawsuits. Warm up your old contacts. You will be fired. Don't get stressed.

Save some more money if you see it coming like this.