Contracts in baseball are used to hire coaches, umpires, players, and administrative and team staff. Contracts are also used to secure television deals, where certain networks are contracted to air baseball games on television. Many of the rules and regulations regarding major league contracts in baseball are controlled by the Major League Baseball Constitution, which has been revised and amended many times since it's adoption in 1876. The Commissioner of Baseball is responsible for hiring the umpires who work for the Major League Baseball Association for both the National and American League. The Commissioner of Baseball also negotiates television contracts, marketing contracts, and general labor contracts related to major league baseball. Sports agents are often used by baseball players in order to negotiate the terms of their baseball contracts. Agents may negotiate signing bonuses, which are paid to players upon signing a baseball contract, as well as many other specific contract clauses relating to everything from special perks to a player's promised yearly salary.