A number of legal challenges also threaten the industry.
Last week a prominent Saudi activist and the non-profit Electronic Frontier Foundation sued DarkMatter, alleging the group hacked into her phone.
Apple sued NSO Group in November, saying that it violated U.S. laws by breaking into the software installed on iPhones.
A 2019 Reuters investigation, cited in the letter, also exposed a secret hacking unit within DarkMatter, known as Project Raven, that helped the UAE spy on its enemies. In a September settlement with the Justice Department, three members of that unit, all former U.S. intelligence operatives, admitted to breaking hacking laws.