Argument from Authority/Appeal to Authority
Wikipedia said:An argument from authority (argumentum ab auctoritate), also called an appeal to authority, or argumentum ad verecundiam, is a form of argument in which the opinion of an authority on a topic is used as evidence to support an argument. Some consider that it is used in a cogent form if all sides of a discussion agree on the reliability of the authority in the given context, and others consider it to always be a fallacy to cite an authority on the discussed topic as the primary means of supporting an argument.
I'm inclined to go with Carl Sagan on this one (emphasis mine):
"One of the great commandments of science is, 'Mistrust arguments from authority'. (Scientists, being primates, and thus given to dominance hierarchies, of course do not always follow this commandment.) Too many such arguments have proved too painfully wrong. Authorities must prove their contentions like everybody else."