I believe it actually is illegal, via a set of more general rules on data collection, on what constitutes a fraud, etc. May not be spelled out exactly like this specific use case, but still very likely covered by law. Just difficult to prove.
It certainly would be illegal in Europe under the GDPR - data collected for one purpose (handling of applications) cannot be used for another without explicit, informed consent.
Don't ignore free speech of job search applicants .!
I saw this post on reddit where some sketchy AI company (Alpheva AI) is posting jobs and requesting a screenshot of all applicants having left their app a 5-star review in the app store as part of the application process:
https://www.reddit.com/r/recruitinghell/comments/1pp0iej/thi...