WASHINGTON — In an unexpected move, President Barack Obama has declined to sign legislation renewing sanctions against Iran but has let it become law anyway.

Obama faced a midnight deadline to sign the 10-year renewal of the decades-old sanctions law. The White House had said that Obama was expected to sign it.

But White House press secretary Josh Earnest says Obama is letting it become law without his signature, saying Obama retains authority to waive all nuclear sanctions lifted as part of the deal reached with Tehran.

Iran’s president had vowed to respond if the sanctions were renewed, arguing they violate terms of the nuclear deal. The White House disagreed but said Obama would sign it begrudgingly despite deeming it unnecessary.

President-elect Donald Trump has been sharply critical of the nuclear deal.