We recently completed a stay where the deposit (paid 60 days prior to check-in) was paid on one credit card and at check-in, the remaining nights and incidentals were applied to a second credit card.

There were a couple of issues at check-out where deposits were incorrectly applied, etc., but they were all fixed quickly.

A couple of days later, I get an email from an accountant saying "Per request of our Hotel Assistant Controller, I am sending a credit card authorization form. Please fill it up for each credit card used to pay for the rooms. Attach a copy of each credit card, to be in compliance with the IRS."

The reservation is exempt from sales tax, so that's the only reasoning I can imagine the IRS comes in to play. I've asked for clarification, but haven't heard back yet. Why would they need a copy/photograph of the physical card when both cards were swiped and viewed at check-in and check-out?

If a reservation is exempt from tax in some states it has to be paid for by a card with the name of the organization on it, not an individual's card. They need a copy of the card showing the name of the organization as proof for the state to show it was allowed to be exempt.

Given the issues you had, they are well within their rights to request the authorization.

Are you sure it's not a scam email? I would be hesitant to blindly send a copy of my credit cards through the email.

Not a scam. It came from the accountant who I'd been dealing with on the phone to fix the earlier issues.

The property likely should have collected this information at check-in (or before). But, if it did not and you swapped cards, it has an obligation to collect the information in order to preserve your tax exempt billing. If you are concerned about method of transmitting, I would send the forms and the card copies in separate envelopes.

That appears to be what happened... the info was not collected by the check-in agent.