http://en.wikipedia.org/wiki/Collective_bargainingThe right to collectively bargain is recognised through international human rights conventions. Article 23 of the Universal Declaration of Human Rights identifies the ability to organise trade unions as a fundamental human right. Item 2(a) of the International Labour Organization's Declaration on Fundamental Principles and Rights at Work defines the "freedom of association and the effective recognition of the right to collective bargaining" as an essential right of workers.
http://topics.law.cornell.edu/wex/collective_bargainingThe main body of law governing collective bargaining is the National Labor Relations Act (NLRA). It explicitly grants employees the right to collectively bargain and join trade unions.
The NLRA establishes procedures for the selection of a labor organization to represent a unit of employees in collective bargaining. The act prohibits employers from interfering with this selection. The NLRA requires the employer to bargain with the appointed representative of its employees. It does not require either side to agree to a proposal or make concessions but does establish procedural guidelines on good faith bargaining. Proposals which would violate the NLRA or other laws may not be subject to collective bargaining. The NLRA also establishes regulations on what tactics (e.g. strikes, lock-outs, picketing) each side may employ to further their bargaining objectives.
State laws further regulate collective bargaining and make collective agreements enforceable under state law.