CAO means collective bargaining agreement
A Cao is a collection of agreements between employers and employees. It complements the existing contract of employment which has been concluded. In the media there is often a difference between Cao and Cao. When it is written with capital letters (CAO) it is about a specific CAO (for the metal industry, the construction, etc. When using lowercase letters is about a CAO in general.
A CAO has a maximum validity of 5 years. At the end (representatives) of both the employer and the workers will negotiate the conditions of the new CAO. It is common for these two parties not to come together and strikes. Often, the agreements of the CAO are more favourable (for the employee) than prescribed in the law. You can think of more holiday days, higher wages, etc. However, it must never be lower than that prescribed by law.
For more information about the CAO, go to the website of Postbus51.