BEIJING, Sept. 27 -- China's top economic planner said Wednesday it had fined 18 manufacturers of poly vinyl chloride (PVC) a total of 457 million yuan (69 million U.S. dollars) for manipulating market prices.

The 18 companies collaborated to raise PVC prices in 2016, causing obvious price hikes in the market, the National Development and Reform Commission (NDRC) said.

Their behavior harmed the market competition order, the profit margins for downstream PVC users and consumers' interests, said the NDRC.

Each of the 18 companies was required to pay between 1 and 2 percent of their annual revenue as a fine.

These companies' PVC production accounted for three quarters of the country's total last year.

They reached 13 price monopoly agreements.

Hubei Yihua Group and China National Salt Industry Corporation Jilantai Salt Chemical Group played a leading role and proposed six meetings to discuss price hikes.

PVC products are widely used in building materials as well as medical and household appliances.