An employee is refusing work?

Then you should issue the employee with a written warning.

The answer in detail
Refusal to work applies when an employee refuses to do the work assigned to him. All activities generally include so-called secondary duties. For example, a truck driver can be required to carry out small repairs to his vehicle himself. Here you'll find a sample letter showing how to formulate a written warning.
Important documents
allgemeiner rechtlicher Hinweis Verwarnung
Vorlage Verwarnung Arbeitsverweigerung