Incorrect, the prohibition is federal.

https://www.atf.gov/firearms/docs/open-letter/all-ffls-sept2...

Yes, it's prohibited at the federal level, but the state laws on that vary, and the states are generally the ones doing the enforcement. An example, in Mississippi (http://billstatus.ls.state.ms.us/documents/2022/pdf/SB/2001-...):

> A registered qualifying patient or registered designated caregiver shall not be denied the right to own, purchase or possess a firearm, firearm accessory or ammunition based solely on his or her status as a registered qualifying patient or registered designated caregiver. No state or local agency, municipal or county governing authority shall restrict, revoke, suspend or otherwise infringe upon the right of a person to own, purchase or possess a firearm, firearm accessory or ammunition or any related firearms license or certification based solely on his or her status as a registered qualifying patient or registered designated caregiver.

Edit: By enforcement, I mean that it's not going to be the FBI or the ATF that knocks on your door if it's discovered you have purchased a firearm with a medical marijuana card but the state, county, or municipal police. The feds might go after the store, though.

No, the ATF will absolutely go after the individual if you lied on the federal form.

The ATF isn't investigating every form to determine if you lied. Nor are the forms always used for firearm purchases.

They don't investigate every form. But there's still a chance. Especially since they're copying books wholesale these days.