According to the latest data available, China’s imports of North Korean goods fell by more than 30 percent in May from a year ago, after Beijing banned coal purchases from the neighboring country, Reuters said.

China’s customs department issued an official order on April 7 telling trading companies to return their North Korean coal cargoes, Reuters reported last month

By halting those coal shipments, China has hampered Pyongyang’s effort to raise hard currency through the sale of one of the country’s exports.

Despite the shrinking trade volumes, China remains North Korea’s largest trading partner, by far, accounting for roughly 85 percent of overall volume in 2015, according to data from the United Nation’s Comtrade database.