The White House announced on November 6, that President Donald Trump has renewed the national emergency regarding Iran, which was put in place on November 14, 1979, at the onset of the U.S. embassy hostage crisis.

The emergency was declared to allow the president to use a federal law, which was adopted in 1977, called The International Emergency Economic Powers Act (IEEPA).

The IEEPA authorizes the president to declare the existence of an “unusual and extraordinary threat…to national security, foreign policy, or economy of the United States”, originating in whole or substantial part outside the U.S.

In 1979, President Jimmy Carter perceived Iran's hostage taking as such a threat and declared a state of emergency.

The White House notice signed by president Trump says, “Our relations with Iran have not yet normalized, and the process of implementing the agreements with Iran, dated January 19, 1981, is ongoing”.

These agreements refer to a deal known as the Hostage Agreement, mediated by Algeria, that secured the release of U.S. embassy hostages in exchange for transferring Iran’s frozen assets in the U.S. to escrow accounts at the Bank of England, while disallowing U.S. nationals from pursuing any legal action against those assets.

This was a controversial issue, challenged by claimants, which eventually reached the U.S. Supreme Court a few months later. The court ruled in favor of the president’s powers to have concluded such an agreement, in the Dames & Moore v. Regan case.

The Hostage Agreement was actually finalized on the last day of Jimmy Carter’s presidency. The next day, when the newly elected Ronald Reagan was taking oath of office, the U.S. hostages were boarding a plane in Tehran, after 444 days of captivity.

Now, President Trump says that because the implementation of the Hostage Agreement is still ongoing the emergency measures adopted in 1979 are renewed for one more year.

“I am continuing for 1 year the national emergency with respect to Iran declared in Executive Order 12170”, the White House announcement says.

The Iran emergency act is the oldest running U.S. emergency measure, which has been renewed every year.