Collective bargaining is a type of negotiation used by employees to work with their employers. During a collective bargaining period, workers’ representatives approach the employer and attempt to negotiate a contract which both sides can agree with. Typical issues covered in a labor contract are hours, wages, benefits, working conditions, and the rules of the workplace. Once both sides have reached a contract that they find agreeable, it is signed and kept in place for a set period of time, most commonly three years. The final contract is called a collective bargaining agreement, to reflect the fact that it is the result of a collective bargaining effort.
Here is a good link regarding the legal issues surrounding collective bargaining.