HONG KONG — Two House Republicans have questioned a prominent American environmental group, contending that by praising China’s efforts to reduce pollution while criticizing American shortcomings it could be working as an agent of Chinese influence.

A June 5 letter from two leading Republicans on the House Committee on Natural Resources to the nonprofit environmental group, the Natural Resources Defense Council, requested documents on its relationship with the Chinese government and answers to questions on whether it should register as a foreign agent.

The N.R.D.C., which was founded in 1970 and now has about 2.4 million members, has fought efforts to scale back environmental protections in the United States, suing the Trump administration about once every 10 days, according to N.R.D.C. officials. The group has also worked for years in China to improve the country’s air quality and reduce carbon emissions.

The letter, from Rob Bishop, a Utah Republican and chairman of the House Committee on Natural Resources, and Bruce Westerman, an Arkansas Republican and chairman of the panel’s subcommittee on oversight and investigations, suggested the difference between the group’s aggressive stance in the United States and a more moderate tone in China meant it was serving Beijing’s interests. The letter was addressed to Rhea Suh, the N.R.D.C.’s president.