The workers at a gas tank factory in Dinslaken, Germany, had questioned the strange goings-on at their company ever since its Iran-linked owners bought it a decade ago. On Tuesday, they got an answer.

The U.S. Treasury Department announced that MCS International, along with companies in Croatia, Dubai and elsewhere, had been part of a global network of 37 businesses designed to funnel profits and materials to the Iranian government and to evade sanctions targeting the country’s nuclear program.

The order, which places trade restrictions on the companies and on any individual or entity doing business with them around the world, is the latest of several efforts announced in the past week to curb trade with Iran-linked groups.

“Even as economic conditions in Iran deteriorate, senior Iranian leaders profit from a shadowy network of off-the-books front companies,” the undersecretary for terrorism and financial intelligence, David S. Cohen, said in a statement.

The Treasury Department said the companies were part of a group called the Execution of Imam Khomeini’s Order that sent billions of dollars in profits back to Iran’s government every year.

But the companies have been so skillful at operating within legal bounds that as recently as April, German and Belgian security authorities allowed a shipment of high-pressure gas tanks from MCS International to Dubai-based Golden Resources Trading Co., another firm on the U.S. list. Trade authorities had delayed the shipment and searched it for possible violations of restrictions on technologies with a dual civilian and military purpose. They found no violations, and MCS International’s management denied having any connection to the Iranian government.

MCS ended production at the end of March after years of unprofitability. Workers said their managers appeared uninterested in the business side of the company and instead focused on using technology from the plant to create a similar factory in Iran.

Nuclear experts say the high-strength carbon fiber used at MCS to make lightweight high-pressure tanks is also useful for building precision centrifuges and missiles.

A spokesman for the German agency charged with investigating violations of trade sanctions had no immediate comment Tuesday.