"We are writing today to specifically inquire about reported negotiations between Russia and certain countries over sales of the Russian government’s S-400 air defense system and whether these reported deals could trigger mandatory CAATSA sanctions," the letter said on Friday. "Under any circumstance, a S-400 sale would be considered a 'significant transaction' and we expect that any sale would result in designations."
The lawmakers also requested that the State Department provide detailed analysis on the current status of Russian S-400 talks with China, Turkey, India, Saudi Arabia, Qatar, and any other country.
The senators based their letter on a report produced by the Congressional Research Service, which showed that Russia has been working on potential defense deals with different countries.
The request comes just a day after the Treasury Department used the CAATSA legislation, along with an Executive Order that was amended by CAATSA, to impose sanctions on five entities and 19 individuals.
Russia's Federal Security Service (FSB), Main Intelligence Directorate and six Russian individuals were sanctioned under the CAATSA legislation.
The US Congress passed CAATSA last summer in response to allegations that Russia sought to influence the 2016 US presidential election. Trump signed it into law on August 2.
Russia has repeatedly denied all allegations of interference in the US election, calling the accusations "absurd."