As various lawyers have commented on Twitter, this seems like an insanely blatant violation of labor laws. Just a straight up written confession of illegal retaliation. Unless they have some obscure exemption that nobody else knows about, I cannot imagine how the university's legal counsel signed off on this.
"Generally speaking, those who are part of a legal strike cannot lose their health insurance or other benefits. While they may not receive them during a strike, these benefits must generally be made available to workers after they return to their jobs."