WASHINGTON — The Foreign Intelligence Surveillance Court ruled late Monday that the National Security Agency may temporarily resume its once-secret program that systematically collects records of Americans’ domestic phone calls in bulk.

But the American Civil Liberties Union said Tuesday that it would ask the United States Court of Appeals for the Second Circuit, which had ruled that the surveillance program was illegal, to issue an injunction to halt the program, setting up a potential conflict between the two courts.

The program lapsed on June 1, when a law on which it was based, Section 215 of the USA Patriot Act, expired. Congress revived that provision on June 2 with a bill called the USA Freedom Act, which said the provision could not be used for bulk collection after six months.

The six-month period was intended to give intelligence agencies time to move to a new system in which the phone records — which include information like phone numbers and the duration of calls but not the contents of conversations — would stay in the hands of phone companies. Under those rules, the agency would still be able to gain access to the records to analyze links between callers and suspected terrorists.