Hong Kong's Democratic Party has asked the anti-corruption agency to investigate the city's chief executive Leung Chun-ying over a $6.4m (£4m) payment he received from an Australian firm while in office.
Leung is facing a political firestorm after the Australian group Fairfax Media reported that the engineering firm UGL Ltd had paid Leung the money in relation to its acquisition of DTZ Holdings, a property consultant where Leung was employed as Asia Pacific director before he assumed the top office in Hong Kong July 2012.
The article, which appeared in several Fairfax newspapers, said Leung had pocketed "millions in secret fees from a listed Australian company in return for supporting its Asian business ambitions".
Leung received the payments in two instalments in 2012 and 2013, while he was serving in office, said the report.
Leung and UGL have both denied any wrongdoing.
A statement from the Hong Kong chief executive's office said: "It is standard practice to pay for such undertakings, as you are requiring the individual to take on obligations and to forgo future opportunities."
Moreover, Leung is facing unprecedented protests over political freedom in the city. Hong Kong has been crippled by massive street demonstrations since late September, after Beijing decided it was to screen candidates for the first election in the territory in 2017.