The Eiger Sanction (1975) on Netflix

A man who was a government assassin who was sent to terminate or as they call it sanction anyone who killed an American agent. His former employer asks him to sanction 2 men who killed an agent. When he refuses, his employer threatens to expose the artwork he has amassed with the money he earned working for them, to the IRS, knowing that he can't account for how he acquired them. So he agrees to one job only which he does. When he refuses to do the second one, a woman he picked up took the money he was paid. Knowing his employer sent her, he confronts the man and tells what he can do with himself. That's when he is told that the agent who was killed is an old friend of his, and the reason why they need him is because he's a mountain climber and the second man though unknown, is part of group who will be climbing the Eiger, which is a mountain that he tried to climb twice and failed. When he accepts after demanding a large fee, his employer tells him that a man whom he has sworn vengeance against though not involved with the death of his friend, so he was not deemed a sanction but he was the one who transported the information that was taken from him so they'll allow him to go after him. So he proceeds to go to a friend's mountain climbing school to train for the climb. While there the man shows up and wants to make a deal with him.