The National Labor Relations Board, also known as the NLRB, is an independent federal agency created by Congress in 1935 to administer the National Labor Relations Act, the primary law governing relations between unions and employers in the private sector. The statute guarantees the right of employees to organize and to bargain collectively with their employers or to refrain from all such activity. Generally applying to all employers involved in interstate commerce, other than airlines, railroads, agriculture and government, the act implements the national labor policy of assuring free choice and encouraging collective bargaining as a means of maintaining industrial peace. Congress has amended the act throughout the years and the board and courts have developed a body of law drawn from the statute. National Labor Relations Board is headquartered in Washington, D.C. It also has a branch located in Philadelphia where it employs nearly 65 people.