Toronto commuters may be in for some TTC turbulence.

The head of the TTC workers union says his members could escalate job action – after what appears to be an organized effort to decline overtime shifts – during the all night Nuit Blanche arts festival .

Union president Bob Kinnear says the mass refusal was “a grass roots movement” – and wasn’t co-ordinated by the union. He says members told him they took action partly in response to the TTC’s plan to eliminate the guard position on some subway trains.

The union is against the move – claiming that removal of the guards will endanger passengers.

For its part, the TTC says transit systems world-wide use one-person train operation – and that it has proven safe.