hold someone's feet to the fire

Also, keep someone's feet to the fire. Pressure someone to consent to or undertake something, as in The only way you'll get him to agree is to hold his feet to the fire. This idiom alludes to an ancient test of courage or form of torture in which a person's feet were so placed. It began to be used figuratively in the second half of the 1900s. Also see hold a gun to someone's head.