WASHINGTON—A mostly Republican slate of 89 members of the U.S. House of Representatives sent a letter to President Obama urging him to fully enforce sanctions on Iran’s Central Bank.

The letter sent Thursday, first reported by the Weekly Standard, was signed by 85 Republicans and four Democrats who emphasized that the president cannot view these sanctions as “advisory only.”

Sanctions on Iran’s Central Bank were approved by the U.S. Senate as an amendment to the National Defense Authorization Act. All 100 senators voted for the amendment, which was sponsored by Sens. Robert Menendez (D-N.J.) and Mark Kirk (R-Ill.).

Following passage of the Defense Authorization Act, President Obama issued a signing statement in which he indicated that he could view the provisions outlining sanctions on Iran’s Central Bank as “non-binding.”

“We respectfully request your administration brief us at the earliest opportunity on how you specifically plan to implement the new sanctions and in particular, how your signing statement and potential reservations will impact the effectiveness of this effort,” the letter said.

A top administration official told JTA that the “non-binding” notification was a pro-forma defense of executive branch foreign policy prerogatives and noted that there were many other such notifications for the overall bill.

The administration, the official said, already has instituted the provisions of the amendment. The official said that advisories were sent out to ambassadors around the world on the day that Obama signed the bill asking them to warn their host nations of the consequences of not abiding by the sanctions.

The White House has 180 days to fully implement the bill’s sanctions or to notify Congress of waivers. However, reports have indicated that the warning of impending sanctions has already had an effect, with countries that trade with Iran turning to other sources, and with a substantial drop in the value of the Iranian rial.