A collective bargaining agreement is a written contract between an employer and a trade union that represents the employees at the company. The agreement covers all aspects of working conditions including hours, rate of pay and job duties.
The employer is obligated to abide by the collective bargaining agreement, and if the employer institutes changes that are contrary to the agreement, a strike would be arranged by the trade union until terms were agreed.
The collective bargaining agreement is the core contract between employers and trade unions, and is the foundation of the obligations that the union has to its members. The union is paid to be responsible for the conditions under which employees work at their place of employment.
If the union cannot enforce the collective bargaining agreement with an employer, then they would not be of value; therefore strikes are instituted to act as the greatest leverage that the trade unions have. By stopping work, unions are able to force employers to abide by the terms of the collective bargaining agreements.