If it's an FR, they'll cut off your card and require you to consent to them checking your tax returns. You'll also be assigned a rep that will handle your case.
I was also in the same boat, sort of. I drew income off a trust during my time in law school and had no idea if it was included on my tax return. I told them that, but they said it didn't matter, all they cared about was my return.
My cards were left untouched, but I don't know why. I am pretty sure I also included all household income when I got my cards a year prior, which was much different than what I made.