If you are a union representative in the public sector you have an extended term of notice. The extended term of notice is the individual term of notice plus three months. However, if the dismissal is due to shortage of work, the notice is not extended.
Dismissal of a union representative in the public sector must be justified with "compelling reasons". This means that the dismissal must not be because of your duties as a union representative, and the employer must prove that this is not the case. For example, if it is possible to dismiss another employee (who is not a union representative) than you, the employer must do so.
If the employer cannot prove that the dismissal is based on "compelling reasons", you may be entitled to financial compensation.
Special rules apply to civil servants.
If you are a union representative in the private sector with a collective agreement, the protection may be stated in this collective agreement.
For other union representatives in the private sector, and for chairpersons of academic clubs and company groups, protection depends on whether the company is covered by a collective agreement that stipulates provisions regarding information and consultation of employees, e.g. the cooperation agreement between the Confederation of Danish Employers and the Danish Confederation of Trade Unions.
If such an agreement exists, representatives on the works council have union-representative protection. If there is no collective agreement, chairpersons of academic clubs and company groups have the same protection as union representatives within relevant or similar areas. Contact IDA for a more detailed assessment of whether you have additional protection against dismissal in your specific situation.
The rules are stated in: Information and Consultation of Employees Act (in Danish).