Actually its not prohibited by the TSA, the exact wording is.
Bumpers
76(1) In this section, “passenger car” means a motor vehicle that is designed primarily to transport people and has a seating capacity of 10 or fewer but does not include a truck, a multipurpose passenger vehicle, a chassis cab, a motor cycle or a moped;
(2) A passenger car must have both a front and a rear bumper.
(3) A person shall not install or alter a bumper on a passenger car unless the design of the bumper is equivalent to, and the bumper is mounted in substantially the same manner as, the bumper installed by the manufacturer of the passenger car.
(4) A person shall not alter a passenger car in such a way that the main structural component of a bumper is more than 500 millimetres or less than 400 millimetres above ground level when the passenger car is not loaded.
(5) For the purposes of subsection (4), components that are commonly known as bumperettes or overriders are not part of the main structural component of a bumper or of the projected vertical facing of a bumper.
(6) Subsection (4) does not apply to passenger cars manufactured before April 1, 1976.
(7) A person shall not alter a car manufactured before April 1, 1976 in such a way that the bumper is more than 100 millimetres higher or lower than it was at the time the car was manufactured.
If a cop wanted to be a nit you can argue that I cant lift my Jeep since it raises the main bumper component over 500mm from the ground.
Also you have to consider that "bumper" means the underlying steel structure or "rebar", not the flimsy plastic covering.