Rep. Ted Lieu wants the FBI to brief lawmakers about why the agency didn't inform dozens of former and current U.S. officials that they were the targets of Russian hackers.

Today's letter to FBI Director Christopher Wray comes in response to an Associated Press investigation that discovered the bureau only notified a tiny fraction of people who had their private email accounts targeted by the Russia-linked hacking group Fancy Bear.

Lieu (D-Calif.), a member of the House Judiciary Committee, wrote that "given the FBI's mission of protecting the United States from the malign efforts of 'foreign intelligence and espionage' and 'cyber-based attacks,' the FBI's response to this advanced persistent threat appeared to have been deficient and demands further attention."

"Failing to notify current or former U.S. officials of known cyberattacks hampers their ability to assess and mitigate damage," he added, noting hackers can glean useful data from private email accounts that can then be used for future attacks.

Lieu told Wray it is "unacceptable" that officials learned they had been targeted through news reports, not from the government, especially after Kremlin-backed hackers successfully breached the DNC and Ukranian military forces.

A senior FBI official told the AP that the bureau simply cannot inform everyone on Russia's extensive digital hit list.

"It's a matter of triaging to the best of our ability the volume of the targets who are out there," the official said.