Argumentum ad baculum
Argumentum ad Baculum (argument from force) is the fallacy committed when one appeals to force or the threat of force to bring about the acceptance of a conclusion.
This is an emotional argument, not a logical one. The person making the threat is making no argument for the truth of their claim. This fallacy is related to the argument from adverse consequences (the adverse consequence in question being punishment).
Since this technique is an attempt to intimidate or frighten the target, it is a variety of the appeal to emotion.