Report unsafe construction work?

I witnessed the construction crew at Bank & Riverside cut a light post guy-wire under tension without securing either end. The long end whipped around down the 8ft or so onto the river bike path under Bank which was still open to bikes and pedestrians. The guy who cut it didn't even go check where it fell and they kind of just laughed it off and kept working. Does anyone know where/to whom I should report this? Obviously not an ongoing concern anymore since it's already been cut but clearly this crew is not taking the proper precautions.

Edit: thanks for all the suggestions. It's been reported to the Ministry of Labour & the city.