FRANKFURT — Volkswagen suspended its chief lobbyist on Tuesday amid a growing furor over experiments on monkeys that were meant to promote the virtues of diesel-powered vehicles, but now threaten to further undermine the German car industry and to increase political instability in Berlin.

Thomas Steg, the suspended Volkswagen executive, is a former aide to Chancellor Angela Merkel of Germany. The widening controversy about the monkey research, detailed by The New York Times last week, highlighted what critics have called the overly cozy relationship between the country’s carmakers and the government.

Germany has often balked at efforts to tighten regulations on auto emissions and to improve enforcement, and the latest uproar has put Ms. Merkel on the defensive as she struggles to form a coalition government after winning a narrow plurality in elections late last year.