The employer is also obliged to make sure that the employee has a valid work permit, before employing a foreign worker.

The validity of the work and resident permit will be stated in the decision. Other conditions of the permit will also be stated in the decision. 

Persons who have lived and worked in Norway without residence and work permit have violated the Immigration Act, and can be deported/expelled from Norway. A foreign natinal who has received a decision on expulsion can appeal against the directorate of Immigration's decision. If you appeal, your application will be re-examined by the UDI. UDI may overturn the decision and grant the requested permit. If  UDI upholds the decision, the case is sent on to the Immigration Appeals Board (UNE) for new consideration.

Working illegally can result in criminal liability both for the employee and the employer. It is, however, up to the police to prosecute. 
 
Expulsion from the Schengen area
A decision on expulsion means that you must leave Norway and are not permitted to re-enter the country.  It also implies entry prohibition to all the Schengen countries. The validity of the expulsion period will be stated in the decison. The authorities in the individual Schengen countries can give separate permit for entry during the expulsion period.