(Yicai Global) July 24 -- TTK Express Co., a Chinese courier firm, has complained to the country's State Post Bureau after online retailer JD.Com [NASDAQ:JD] ordered sellers to use other delivery services.

The e-commerce giant issued a notice to merchants on July 19, requiring them to switch couriers before July 25. Service quality and a violation of the platform's rules were cited as the reasons for the decision after JD received a number of complaints.

"It has seriously infringed on our reputation and on vendors' right to choose," TTK said in a statement, adding that JD hadn't communicated any difficulties prior to the move or sought a more effective solution.

TTK has worked with JD for five years, it added, and complaints data from China's postal regulator shows that its service quality has risen rapidly in the first half of this year.