BEIJING, May 18 -- The Chinese Ministry of Commerce made a preliminary ruling on Monday that Japanese and U.S. companies are dumping optical fiber preforms and will impose provisional anti-dumping measures.

A probe, launched on March 19 in 2014, found that their dumping activities were damaging the interests of Chinese optical fiber producers, and that there was a causal link between the dumping and the damage caused.

The ministry told domestic importers of the products to pay cash deposits to customs. The deposit rate ranges from 7.8 percent to 39 percent of the value of their imports.

Optical fiber preform is a piece of glass used to make optical fiber.