No law that i know of. Price fixing is when you and your competetors get toghter and agree what each of you will bid on a job Prior to the bid opening. Knowing what you competetion charges allows you to be competive in the market you are in. As long as you do not discuss your price for a job ahead of a bid with your competetor you should be ok. After the bid is opened we all should be able to see where we stand.
