greymail
/ˈɡreɪmeɪl/noun
1A mild form of blackmail without demands for money; exercise of power over a person through possession of compromising information.
2 US Law. The threat of revealing government secrets, made by an accused party (especially in cases of espionage) as a strategy to avoid prosecution.
Origin
1920s; earliest use found in Osbert Sitwell (1892–1969), writer. Punning alteration of blackmail, after grey.