Any one who does "significant" business with the 39 firms could find themselves facing sanctions according to the law that President Donald Trump signed in August.
The US State Department on Friday named 39 Russian defense- and intelligence-related entities under a new sanctions law, belatedly taking a step to enforce legislation passed overwhelmingly by Congress.
The law, which President Donald Trump signed on August 2, requires sanctions on individuals who engage in "a significant transaction" with the Russian entities.
Friday's action does not itself impose new sanctions, and determinations will be made on a case by case basis, State Department officials said.
Both Republican and Democratic lawmakers have complained that Trump has been tardy in enforcing the law, which required the list of Russian entities be ready by October 1.
The list includes major Russian arms makers as well as Rosoboronexport, the state-run Russian arms exporter. Also listed is the St. Petersburg-based Special Technology Center, which former President Barack Obama sanctioned in December, saying it played a role in Moscow's hacking and other interference in the 2016 US presidential election.
Russia has denied such meddling.
State Department officials, who briefed reporters on condition of anonymity, indicated the Trump administration would move carefully in imposing sanctions and dealing with issues such as US allies who buy Russian-made weaponry or spare parts.
"There is a significance threshold that would exclude certain things that are less than significant," one official said. "Obviously we’re going to consider the totality of circumstances."
State Department guidance released on Friday says that in determining whether a transaction is "significant," officials would weigh its impact on U.S. national security; its size and scope; and the importance of the deal to Russia's defense and intelligence sector.
The law requires Trump to impose sanctions by January 29 on transactions that are found to meet the definition and which took place after he signed the legislation in August.
"We'll be implementing the sanctions legislation robustly, in keeping with our understanding of Congress’ intent and the facts that precipitated that legislation, including interference in our election," a second State Department official said.
The same official did not dispute a report that Secretary of State Rex Tillerson had eliminated a department office charged with coordinating economic sanctions. The office traditionally had been led by a senior US diplomat.
The official added that individuals throughout the department work on sanctions and that coordination of such work would continue.