WASHINGTON — Many U.S. multinational corporations have packed up or are choosing to open subsidiaries in low-tax, rather than no-tax, countries that are seen as more legitimate than the formerly popular island destinations of the Cayman Islands and the Bahamas.

They’re fleeing in response to regulations from the European Union that require them to justify the business purpose for their offshore operations. Low-tax countries that have been attractive destinations for multinationals — such as Singapore, Ireland and the Netherlands — are becoming even more desirable, especially as they make changes to show they’re more legitimate.

“The days of picking a holding jurisdiction mainly because of tax are over,” said Allen Tan, head of the tax practice at law firm Baker McKenzie Wong & Leow in Singapore.

American corporations have used tax havens for years to avoid higher levies where they earn their income. European countries and the U.S. have teamed up in recent years to stop the use of loopholes and collect more of the taxes the companies headquartered within their borders owe.

Insurance firm Swiss Re AG closed one of its Bermuda subsidiaries in 2016. It opened its regional headquarters in Singapore in January.

The company said in a statement that it doesn’t use tax havens for the purpose of avoiding tax and that the entities registered in Bermuda are fully taxable in the U.S.

Facebook Inc. has said it plans to almost triple its workforce in Singapore. The social media company reports only Irish and Singapore subsidiaries, according to a 2017 study by the left-leaning Institute on Taxation and Economic Policy.

The company said last year that it was changing its sales structure so income is booked in the country where it’s earned. Facebook has until 2020 to wind down transactions in which it routed income from Irish subsidiaries to the tax-free Cayman Islands.

Countries like Singapore that are more developed and still offer relatively low tax rates are seizing the moment, highlighting their infrastructure, available labor forces and tax agreements with other countries.

Tax experts say the driving force behind the move away from the most flagrant tax havens is a series of requirements from the Organization for Economic Cooperation and Development intended to stop companies from shifting profits abroad.

The standards, which have become law in many European countries, require companies to show economic substance — employees, management teams and sales — in the countries where they earn income.

Tax authorities in OECD countries also have to exchange data annually with each other about how much companies earn, how much tax they pay and how many employees they have within their borders. The first data swap occurred in June.

Two of the most egregious tax moves — the “Double Irish” and the “Dutch Sandwich” — that often involve using zero-tax havens as the destination for offshore income were effectively killed by OECD rules, though some companies like Facebook have a couple of more years to end the practice.

The Internal Revenue Service is planning to issue rules soon that would implement some of the OECD requirements.

Alphabet Inc.’s Google moved $18 billion to Bermuda in 2016 to shield much of its international profits from taxation, according to a 2018 regulatory filing in the Netherlands.

With those transactions “income essentially falls into the ocean because nobody is taxing it,” said Jeffrey Korenblatt, a tax attorney at law firm Reed Smith.

Now, companies in the technology and pharmaceutical industry that were the most frequent users of the tactics are forced to keep that income within the initial European country. In turn, Ireland and the Netherlands are tightening their accounting guidelines and making it more difficult for companies to massage their numbers about where income is earned.

Still, some firms — such as hedge funds — are staying put in their Caribbean locations, undeterred by political pressure and facing fewer restrictions since many are private.

Other European countries, such as Switzerland, are trying to make sure they aren’t blacklisted. The EU put Switzerland on a “gray list” of jurisdictions with questionable tax regimes last year. Now the country is working to change its corporate tax system.