However, to qualify as a collective agreement, the contract must also meet certain formal requirements. The contracting parties must be organisations in full legal capacity and the agreement must be notified to the Ministry of Social Affairs.  If the agreement does not contain these elements, it may still be legally binding, but it will not produce the special effects conferred on collective agreements by the 1927 Act. If the parties have no intention at all of creating a legally binding instrument, their agreement can only be a gentlemens agreement. Disputes concerning the characterization of agreements between trade unions and employers have arisen mainly in the field of enterprise restructuring. Agreements containing social plans for collective redundancies or restructuring agreements are not always considered to be collective agreements within the meaning of the 1927 Act.  In Dutch law, a distinction must be made between a formal concept of collective agreement and a concept of a substantive collective agreement. The material concept of the collective agreement is very diverse. The Collective Agreements Act provides that a collective agreement is an agreement between one or more employers or one or more employers` organisations and one or more workers` organisations which contain mainly or exclusively provisions on working conditions to be respected in individual employment contracts. This description of the collective agreement, which results from the period of adoption of the Collective Agreements Act in 1927, has not proved, over the years, to be a real limitation of the powers of the social partners. The concept of a collective agreement includes both sectoral agreements and agreements between trade unions and a single employer. It applies to collective agreements, which contain provisions on a large number of subjects, as well as to specific agreements on a single subject. In principle, all elements of labour law conducive to negotiation between trade unions and employers may be the subject of a collective agreement within the meaning of the law.  As a general rule, a collective agreement is binding on the contracting parties and each member of the treaty. This means that the employer and the worker are bound by a company agreement if they are members of the organizations (which were or were at the time of the conclusion) that are parties to the agreement.  Collective agreements are void and are automatically replaced by the corresponding provisions of the collective agreement.  Gaps are automatically filled by collective provisions. In this way, the individual agreement is inspired by the collective agreement. The individual worker can (and must) rely on this remodeled individual agreement if he or she wants to obtain benefits from the employer. If this theory of creation is not sufficient to ensure application, the worker can sometimes rely directly on the collective agreement itself. A good example of the latter mechanism is a case that came to the Supreme Court and looked at the probationary period.
Under the corresponding collective agreement, each trial period had to be the subject of a written agreement, adding a form to the legal requirements of the Civil Code. According to the Supreme Court, the requirement of the collective agreement invalidated an orally agreed probation period. As such legislation cannot be regarded as included in the individual agreement, the individual worker had to base the change in test time on the collective agreement itself. . . .