A bargaining counter - Idioms by The Free Dictionary
a bargaining counter
Something used during a negotiation that provides one party leverage over another party. Primarily heard in UK. Joe's willingness to walk away from the deal proved to be an effective bargaining counter when it came to purchasing a new car.
a ˈbargaining counter (British English) (also a ˈbargaining chip American English, British English ) a special advantage in negotiations, disputes, etc. which can be offered in exchange for something: The proposed troop reductions were a useful bargaining counter in the disarmament talks.