Is the commission paid by suppliers to the accounting employee, in exchange for his continued dealings with them and favoring them, considered permissible or impermissible, especially since the employer aims to obtain the lowest prices?

A commission is not permissible for an employee unless authorized by their employer. This is because it might lead to the employer's rights being diminished due to the employee's favoritism towards the entity paying the commission. The Permanent Committee has issued a fatwa (definition) stating that it is not permissible for a broker who receives a monthly salary to take a commission from another company in exchange for dealing with them to purchase items on behalf of the company he works for, as this could affect the quality or price of the goods.