All perfect praise be to Allah The Lord of the Worlds and may His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
It is permissible for an employee of the private sector to receive the gifts given to him by customers on voluntary basis {without asking, greed or exploitation} provided that the employer approves of that. This is because the employee is an agent and the scholars have disagreed about the ruling on gifts given to the person of such capacity: Is it the right of the agent or the one who had authorized him? To get out of this disagreement, the permission of the employer should be sought.
If the company`s owners stipulated that the drivers give those gifts to the company in order for the latter to divide them amongst all the staff members, then it isn`t permissible for the drivers to take these for themselves; rather they should be handed to the company`s administration. In principle, an employee should adhere to the laws and regulations of the company in which he works. Bukhari related in his Sahih, "The sorting out of claims will be held to their conditions and yours is what you have stipulated." And Allah knows best.