have a hold over (someone)
To use knowledge of one's past behavior or misdeeds as a means of leverage or manipulation. I was a kid when I made that mistake! Just how long do you plan to have a hold over me?
have a hold over
Also, have a hold on. Have a controlling influence over. For example, Blackmailers have a hold over their victims, or, as Shakespeare put it in The Merchant of Venice (4:1): "The law has yet another hold on you." [Late 1500s]