The leaders of the House Oversight and Reform Committee on Wednesday demanded a briefing from the FBI on its decision to withhold for three weeks the decryption key necessary for companies impacted by the ransomware attack on IT company Kaseya to recover.

The request came a week after The Washington Post first reported that the FBI, in consultation with other agencies, chose to hold on to the decryption key as part of a planned effort to disrupt REvil, the Russian-based cybercriminal group behind the attack on Kaseya.

The attack is estimated to have impacted between 800 and 1,500 groups beginning prior to the Fourth of July holiday.

“Although the Federal Bureau of Investigation (FBI) reportedly obtained a digital decryptor key that could have unlocked affected systems, it withheld this tool for nearly three weeks as it worked to disrupt the attack, potentially costing the ransomware victims—including schools and hospitals—millions of dollars,” Committee Chairwoman Carolyn Maloney (D-N.Y.) and ranking member Rep. James Comer (R-Ky.) wrote in a letter sent to FBI Director Christopher Wray Wednesday.