Is it permissible to increase the price of merchandise for the customer in order to receive the agreed-upon salary from the employer who does not pay it in full except upon demand?

Both the employer and the employee must fear Allah and refrain from oppressing or betraying each other. The employer must give the employee their due promptly. The employee is entrusted with their work and is not permitted to neglect it. Any increase beyond the agreed price belongs to the shop owner, not the employee, unless the shop owner withholds the employee's rights and denies them, in which case the employee may take it secretly.