"You can not punch a competitor and particularly not in the face," a race referee said to Norwegian TV2. "It's not good for the reputation of cycling and he cannot take the law into his own hands. So we have taken the decision of taking him out of the race."
Van Hecke, however, told TV2 that the punishment was too extreme and that Boom should be allowed to continue.
"Sometimes this happens in a race. He did not hit my face, but in the hip," Van Hecke told TV2.
Boom defended himself, saying that Van Hecke was coming into his wheel and he hit out to keep from crashing.
"He was on my wheel and I almost crashed, so I got a little hot headed. I don't want to crash, especially when an idiot does something like that," Boom said.
Boom, 32, is making his comeback from cardiac surgery, which he underwent in December to correct an arrhythmia. He has yet to finish a race this season: after an aborted start in Paris-Nice, he dropped out of the Tour de Romandie last month. The latest expulsion will do no favours to his goal of making Lotto's Tour de France squad.
Boom later apologised to cycling fans and the organisers of the Tour of Norway for his actions at the race, in a post on Twitter.