Milwaukee-based Johnson Controls and Tyco International are taking advantage of a tax loophole known as corporate tax inversion. (Mauritz Antin/EPA)

The march of companies abandoning their U.S. citizenship for lower taxer overseas reached a new height Monday when manufacturing giants Tyco International and Johnson Controls said they had agreed to a mega merger.

Tyco and Milwaukee-based Johnson Controls are taking advantage of a tax loophole known as a corporate tax inversion in which an U.S.-based company buys or merges with a foreign company and moves its headquarters to a country with a lower tax rate.

In this case the new company would be called Johnson Controls but would have its headquarters in Cork, Ireland where Tyco is already based. The strategy would save the company—with a market cap of about $36 billion— about $150 million a year in taxes.

This is not the first time Tyco, which started as a New Jersey-based research laboratory for the U.S. government in the 1960s before growing into a global behemoth with workers in about 50 countries, has made use of tax-avoidance measures. In 1997, it merged with a Bermuda-based company in another corporate inversion before moving its headquarters to Switzerland in 2008. It moved to Ireland in 2013.

Each move helped keep the company’s tax rate low. “This is a company that is notorious for using loopholes in the system,” said Frank Clemente, executive director of Americans for Tax Fairness. “They were pioneers.”

While inversions have been around for decades, they have become more common in recent years. The practice, experts have said, diverts billions in tax revenue from U.S. coffers. A 2014 estimate by Congress’s Joint Committee on Taxation projected that inversions would cost the United States $33.6 billion over a decade.

The Obama administration has repeatedly attempted to stem the practice, but failed to make a significant dent. After the Treasury Department announced new measures last year that make it less financially attractive for a U.S. company to move its headquarters to a country where it does little business, companies simply structured the deals differently.

That is what appears to have occurred in the Tyco-Johnson Controls merger. In order to qualify as a corporate inversion, the U.S.-based company involved in the deal, in this case Johnson Controls, must own less than 60 percent of the combined firm.

Under the deal announced Monday, Johnson Control’s shareholders would own just 56 percent of the combined company. But that is in part because they are being paid in cash and not just stock, said Robert Willens, a New York-based tax expert.

“By paying them in a combination of stock and cash it allows them to fall below the 60 percent ownership line,” he said. “That’s important.”

Officials for Johnson Controls, which is one of the world’s largest makers of auto batteries and HVAC systems, said its merger with Tyco was not prompted by the tax benefits.

“This merger is not about the foreign domicile,” Fraser Engerman, spokesman for Johnson Controls, said in an interview. “It’s about our ability to serve our customers and create compelling value for our respective shareholders.”

There’s broad political agreement that action should be taken to curb inversions, but just how to do it is still under debate. Lawmakers remain at odds over whether and how to lower the corporate tax rate of 35 percent, one of the highest rates in the world. Republicans have argued that curtailing tax inversions should be part of comprehensive tax reform, but Democrats have pushed for immediate action while a broader overhaul of the corporate tax code is worked out.

The issue has also become part of the 2016 presidential campaign. In December, Democratic presidential candidate Hillary Clinton proposed penalties for businesses that try to avoid taxes through offshore mergers.

In the meantime, corporate inversions are likely to get bigger and more common, said Willens.

“We did have a lull in inversions and it lasted for several months,” he said. “But now people are pretty comfortable that what Treasury has laid out is all they can do.”

“Now that we know the ground rules, you can plan around them. That is what is happening here.”