Worker combining work with training

An employee who combines work with correspondence courses at a state-accredited educational institution of higher professional education has applied to the employer for the provision of two working days a week 10 months before passing state exams to prepare for exams. The employer established the employee only a seven-hour shorter working week with payment of 50% of the average wage for the time of dismissal.
Is the decision of the employer legal? Give a reasonable legal assessment of this decision.