http://www.thestrad.com/united-airli...ent-violinist/

‘Yennifer Correia…was in the process of boarding her flight from Houston to St Louis when a United supervisor refused to permit her to carry her violin onto the plane,’ ...

‘Without provocation, the supervisor for the Chicago-based carrier then lunged for Ms Correia’s case and, incredibly, tried to wrestle it away from the musician. Ms Correia screamed for help. The United supervisor threatened to “call security” and Ms Correia responded, “Please do!” at which point the United supervisor ran away.’

/////
At what time is it ok for an airline employee to attempt to touch a passenger's bag without permission, when the passenger has not boarded?

(My apologies that I don't know how to italicize the article quotes while posting from my phone.)