Company X is the sole agent of a set of skin care products in Hong Kong. The skin care products are in very strong demand in Hong Kong. Company X has made an agreement with thirty retailers to distribute the skin care products.

All the retailers are required by the agreement (a) to sell the skin care products at a price in accordance with the price list issued by Company X from time to time, and (b) to participate in all the promotional activities arranged by Company X.

Whether the said agreement between company X and the thirty retailers is legal and why?