Bloomberg | Leonid Bershidsky: Keeping the Islamic Republic on the global SWIFT network would defy the U.S. and its sanctions.

The determination of European nations, Russia and China to keep the 2015 nuclear agreement with Iran alive isn�t necessarily futile. Europe has more influence than the U.S. on SWIFT, the Brussels-based global payments network.

The system was�founded in the 1970s�by a group of global banks that wanted to standardize the way they shared transaction information, instead of letting each country, or even big banks, impose their own standards. SWIFT is owned by its members and provides the backbone of modern international banking, carrying more than 30 million transaction-related messages a day among 11,000 banks. Because it is based in Brussels, it is subject to European Union laws. In 2012, the EU�imposedsanctions on Iranian banks, and SWIFT�expelled�30 Iranian members,�including the country�s central bank.�Iranian banks were reconnected to the network in 2016.

With the loss of access to SWIFT in 2012, Iran�lost the ability to be�paid for its exports and to pay for imports. Domestically, Iranian companies had to revert to the old, slow and expensive�hawala�transfer system ��a major inconvenience for ordinary people as well as merchants.

Even though President Donald Trump announced earlier this month that the U.S. was withdrawing from the 2015 pact that eased sanctions in exchange for Iran�s commitment�to curb its nuclear program,�the EU, Germany, France, the U.K., China and Russia�remain�parties�to the deal. This means SWIFT isn�t required to kick Iranian banks off its network again. The cooperative says it�ll be consulting with regulators on both sides of the Atlantic, but it�s highly unlikely it will act unless the EU does.

The U.S. sanctions will inevitably bite and multinationals with U.S. operations won�t be able to invest in Iran, but the Islamic Republic wouldn�t be under life-threatening pressure if it can keep exporting oil. Under the post-2012 regime, barter deals, hawala-style payments and makeshift arrangements involving foreign banks were the only ways to keep exports up, and there were relatively few takers. That�s�a major reason why Iran�s oil and gas export revenue dropped to $52�billion in 2012 from $92.5 billion the previous year and continued falling until the nuclear deal was reached.�Without the removal of SWIFT, the resumption of U.S. sanctions wouldn�t do that kind of damage.

This means Europe ��already locked in a dispute��with the U.S. because of a�threat to impose high tariffs on European steel and aluminum exports ��doesn�t have to take Trump�s Iran move lying down.

If the EU refrains from excluding Iran from SWIFT, the U.S. could sanction the cooperative, but that could prove harmful to American interests as�it would have major consequences for the global financial system.

If SWIFT becomes unreliable, there would be huge demand for alternative transaction information systems such as those offered by blockchain startups and authoritarian states to fill the void.

Russia�and Iran�are already reportedly looking at blockchain-based payment systems as an alternative to SWIFT and as a way to avoid transactions in dollars. Russia has built a SWIFT alternative for domestic use, which it�s beginning to push to banks and firms in the Eurasian Union, a small group of countries that have formed a free economic area with Russia. The system�s attraction is that messages are significantly cheaper than on SWIFT.

Since 2015, China, too, has experimented with a homegrown solution for cross-border payments in renminbi. The system isn�t widely used, but it could work for a country seeking to bypass sanctions. The more trouble for SWIFT, the more attractive the alternatives will become. A return to a pre-SWIFT world, in which banks were forced to send and accept transaction information in�a multitude of formats, isn�t unimaginable.

When alliances crack and rules are redrawn on the fly, global infrastructure that we take for granted is not immune to shocks, even to fragmentation. SWIFT, with Europe�s help, could be able to cling to its neutrality and help preserve the Iran deal until the U.S. is ready to talk sense again.

This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.