Religious most likely
https://slate.com/technology/2015/02/religious-exemption-for...
But it's all irrelevant in this case because Google is almost entirely an at-will employer. They can change the terms of the agreement at any time - take it or leave it.
Hopefully Google will only allow exemptions based on health issues.
My employer mandated vaccines. Exceptions for sincere religious belief or documented medical reasons. I didn't want the vaccine but I wasn't going to lie about having a legitimate religious reason for it. Some people will, but most people wont.
So I got the shot, but if I have any serious side effects I will certainly be contacting a personal injury attorney.