Why hasn't the federal government mandated Form I-9 employment eligibility as part of federal tax returns?

Seems like a more systemic way to improve issues around people overstaying visas or using tourist visas to work (in the formal economy at least).

All employers already are supposed to confirm Form I-9 (but they clearly don't).

Agree. Fines and jail time for employers seem like a more efficient way to enforce immigration laws. I wonder if it is because it’s hard to prove? Maybe many employers just pay cash and leave no evidence?

It’s not intentionally ineffectively enforced to enable big businesses to exploit illegal cheap labor under the threat of deportation. Entrenched interests, lobbyists, and big money have much more influence on immigration policy than who is in power.

It seems using the E-Verify portal to validate Form I-9 employment authorization is only mandated in some states right now.

It seems the others just need to collect the information but not validate it.