Pendle MP Andrew Stephenson has confronted two youths on a train who refused to pay the £1.20 fare.
He was travelling back to Pendle on the Leeds to Skipton train last Thursday when the trouble flared up.
Mr Stephenson told the youths that they risked arrest if they didn’t pay for the ticket after they had kept the busy commuter train waiting for about 15 minutes.
The two youths then paid, but initially refused to get off the train at the next stop in Bingley.
After relenting, they got off, but one of the youths then spat in the ticket inspector’s face.
Mr Stephenson said: “My grandfather was a bus conductor and I don’t know if it was because of that it annoyed me, but it was a natural reaction and I didn’t really think too much about the situation.
“I think it’s absolutely disgusting, it beggars belief.
‘Nobody deserves to be verbally abused in that way, or to be spat at.”