Garden leave describes the practice whereby an employee who is leaving a job (having resigned or otherwise had his or her employment terminated) is instructed to stay away from work during the notice period, while still remaining on the payroll.
If an employee is suspended, or is exempt from work until the end of his employment, but is keeping his salary, the 30% facility for this employee may no longer be used during the period of inactivity.
The 30% ruling ends directly as of the first day of the garden leave. It does not matter that the official employment contract has not ended yet.
The employee will in principle lose the entitlement of the 30% ruling as of the first day of the garden leave. However, if the employee finds a new job within 3 months, the new employer and employee can request for a new 30% ruling for the remaining duration (if the employee still meets all conditions).
Note that Article 10ed of the Wage Tax Implementing Decree 1965 refers to 3 months. No calendar months. Suppose: the start date of the dismissal/suspension/inactivity is 8 September 2020, then the 3-month period ends on 7 December 2020 and a new employment contract must have been concluded before this date. The actual work at the new employer does not need to have started yet.