WASHINGTON – The harshest sanctions towards a regime ever passed by Congress have snapped back into place on Iran and on foreign businesses, after President Donald Trump withdrew the U.S. from the 2015 deal governing the Islamic Republic’s nuclear program.

Trump chose a “hard exit” from the agreement on Tuesday, returning all U.S. sanctions that had been lifted by the nuclear deal at roughly the same time. That will affect billions of dollars in existing contracts between private corporations and Iran, and untold future investments in a country whose currency is already spiraling out of control.

All new contracts will be immediately subject to these sanctions, mostly passed into law in 2012 during an earlier peak in the Iran nuclear crisis. These bills targeted foreign businesses outside the jurisdiction of the U.S. – including some of the biggest companies of America’s closest allies in Europe – by threatening to cut them off from the U.S. financial and banking systems if they invest in Iran.

For existing contracts, companies will have a “wind-down” period of three to six months. All U.S. sanctions lifted under the nuclear deal must go back into effect “in no case later than 180 days,” according to guidance provided to businesses by the Treasury Department. Following November 4, the U.S. Office of Foreign Assets Control “expects that all the U.S. nuclear-related sanctions that had been lifted under the JCPOA [Iran nuclear deal] will be reimposed and in full effect.”

The first wave of these sanctions, which will hit 90 days from Tuesday, will target Iran’s automotive sector, its trade in precious metals, aluminum, steel, coal and carpets, its sale of Iranian rial currency and its maintenance of offshore accounts, its access to the U.S. dollar and those seeking to purchase Iranian sovereign debt.

The larger, more complicated deals will be affected by the November 4 deadline. Iran’s ports and shipping industry, its entire petroleum and energy sectors, and all foreign transactions with the Central Bank of Iran and other Iranian financial institutions will come back under U.S. sanctions.

The latest financial sanctions will affect Iran’s basic ability to conduct trade and make it difficult for other parties to the 2015 agreement – France, Britain, Germany, Russia and China – to keep the agreement alive, if they want continued unobstructed access to U.S. financial institutions.

“The purpose of the wind-down provisions – for example, in the case of oil purchases from Iran, if it’s a long-term requirements contract, for example – what we’re saying is that although the sanctions come back into effect immediately, precluding any new contracts, for those affected by our jurisdiction, they’ve got six months to phase it out,” said John Bolton, Trump’s national security adviser, in a briefing with reporters. “It’s a way to give businesses a chance to get out.”

The U.S. will also reimpose sanctions on specific persons who were targeted for their involvement in Iran’s nuclear program, relieved of sanctions since January 16, 2016, when the nuclear deal was implemented.

EUROPEAN BUSINESSES will face the greatest backlash, having invested heavily in Iran’s automotive, aviation and oil and gas sectors since the deal went into place. They are now in a limbo period as their governments insist the agreement is still in effect, while U.S. ambassadors warn them to exit the Iranian market fast, as Trump’s new envoy to Germany exclaimed on Tuesday.

The European Commission says that U.S. “extraterritorial,” secondary sanctions affecting businesses outside of U.S. jurisdiction are illegal under international law, and has passed “blocking” legislation that will attempt to shield businesses already working with Iran. It has also discussed extending emergency credit lines to businesses that will come under sanctions.

But when last faced with secondary sanctions on Iran, in 2011-2013, European governments chose not to fight them and instead to join the U.S. with sanctions of their own. This is the hope of the Trump administration: that the EU will not engage in a trade war for access to the Iranian market, and instead cave in to U.S. sanctions threats by abandoning the nuclear deal.

But there is no evidence that European leaders have an interest in this approach.

“It’s too complicated if you make war against everybody,” France’s president, Emmanuel Macron, told Fox News last month, visiting Washington in an effort to keep Trump in the deal. “You make trade war against China, trade war against Europe, war in Syria, war against Iran.”

“Come on,” he said. “You need allies.”

Even if EU businesses do choose to pull out of Iran, competitors from Russia and China – which were last to join the 2011-2013 international sanctions regime – may simply fill the void. If France’s Total SA oil and gas giant were to exit, for example, China’s top oil and gas company CNPC might simply take over its stake in the unfinished project, industry sources say.

U.S. businesses will also be affected by the sanctions, although they represent a small portion of the investment rush that Iran enjoyed in light of the nuclear deal. In particular, Boeing, which agreed in December 2016 to sell 80 aircraft, including 15 Boeing 777-300ER long-range jets, to Iran Air, says it is approaching the Treasury Department for clarity on how to proceed.

The Boeing-Iran deal is worth an estimated $20 billion. “Following today’s announcement, we will consult with the U.S. government on next steps,” the company said, following a dip in its stock price.