An agent tried this one morning on me at DFW before I had CLEAR. She said I couldn't use the First Class line and had to use the 30 min long precheck line, even though I was in First Class. I told her she was wrong and given incorrect information, and as a First Class passenger I was entitled to the line. She let me through but said "TSA will turn you around immediately". She was completely wrong. TSA agents couldn't care less as long as they get an ID that matches a boarding pass - you're through.