Television Broadcasts, or TVB, Hong Kong’s dominant free-to-air TV broadcaster, has revealed that it has received a proposal from a mysterious investment company offering to buy a 29.9% stake.

The surprise announcement comes only a few months after Chinese media mogul Li Ruigang was approved as TVB’s vice chairman. It is certain to fuel suspicions that the Chinese government is trying to use corporate channels to undermine Hong Kong’s free-wheeling media outlets.

TVB suspended its shares from trading on Wednesday morning. Later in the day it disclosed the unsolicited offer from TLG Movie and Entertainment Group to buy a 29.9% stake, which would cost US$501 million (HK$3.89 billion) at the suspension price. TVB is valued at US$1.68 billion (HK$13 billion).

In a two-page letter to TVB shareholders, the companies said TLG’s purchase is conditional on TVB canceling a share buyback that the broadcaster proposed in January at a price of HK$30.5 per share. It also said that the purchase needs the approval of Hong Kong’s broadcast regulator, the Communications Authority.

Mystery surrounds the identity of TLG, which describes itself as being “engaged in the cultural industry and real-estate development and investments.” Although Hong Kong public broadcaster RTHK described TLG as a Beijing-based company, public records show that it is a Hong Kong-registered private firm established in August 2015. It has two shareholders and just one company director, Kelvin Dong Wei-tsun.

TVB was founded in 1967 by the late film mogul Sir Run Run Shaw, and currently operates five TV channels. Shaw’s widow, Mona Fong, remains a non-executive director and a major shareholder.

The company’s dominance of TV in Hong Kong was strengthened last year by the collapse of its biggest rival, Asia Television, and by the disarray of the government’s attempts to foster a new digital broadcasting sector. Despite its position and its ownership of one of the largest libraries of Chinese-language content, TVB has begun to struggle. In January, it announced that it would quit the loss-making, pay-TV sector.

Last year, Li, who is the former head of Shanghai Media Group and current chairman of China Media Capital, was given special clearance by the Communications Authority to become a major share owner and a TVB company director. Li is a director of Young Lion Acquisition and Shaw Brothers, two companies that control 26% of TVB shares.

Li’s growing clout at TVB, the acquisition last year of the South China Morning Post by China’s Alibaba, and other Red Capital moves have many in Hong Kong’s media sector worried that the territory’s autonomy, including freedom of the press, is being eroded. In its latest report, the non-governmental organization Reporters Without Borders said that “Beijing’s influence is increasingly noticeable” in Hong Kong’s media.

TVB and China Media Capital are also joint venture partners with Warner Bros. in Flagship Entertainment, a Hong Kong-domiciled, Beijing-based company aimed at producing Chinese and global blockbuster films.