Ropes & Gray will lead an internal investigation at British pharmaceutical giant GlaxoSmithKline Plc. (GSK), following Chinese government allegations that the company’s China operations paid almost $500 million in bribes to help boost sales.

GSK has admitted that some of Chinese employees may have broken Chinese laws. China's Ministry of Public Security has said it believes GSK paid bribes to doctors and other officials to get them to use its products over those of competitors. Chinese police have detained four Chinese executives from GSK, including the company’s China legal affairs director Zhao Hongyan.

A U.S. spokesman for the Boston-based law firm confirmed the representation Thursday. Ropes & Gray Shanghai managing partner Arthur Mok said the firm has an existing relationship but declined to elaborate. According to its website, Ropes & Gray has around 20 lawyers in its Shanghai office, which opened in 2011.

Ropes & Gray previously acted for GSK in 2011 when it was part of the team that successfully defended Lauren Stevens, a former in-house lawyer at the company, against charges that she had lied to and obstructed the U.S. Food and Drug Administration in the course of an inquiry into the marketing of the antidepressant Wellbutrin.

Beijing-based Jun He Law Offices is advising GSK in the ongoing investigation by the Chinese government. Zhang Wen, head of litigation at Jun He said her firm has previously advised GSK on its China ventures but declined to comment further on the matter.