In connection with the reorganization of the printing

In connection with the reorganization of the security system of the printing house, all the guards were transferred from a two-shift operation to a three-shift operation. Zhigunov and Petrovets refused to work in the new conditions under the pretext that the employer did not receive the consent of the workers to change the work and rest regime and did not ask the opinion of the trade union committee in this regard. For failure to fulfill the order, employees were reprimanded with a warning about the subsequent dismissal in case of disobedience to the employer.
Evaluate the lawfulness of the penalty. In what order can an employer change working hours?