The European Union’s antitrust body has launched a probe into U.K. tax rules that allegedly help multinational companies to pay less taxes in Britain, the European Commission said on Thursday.

The competition watchdog said it will investigate whether a U.K. tax scheme is in breach of EU state aid rules, by exempting transactions by multinationals from anti-tax avoidance rules.

“All companies must pay their fair share of tax. Anti-tax avoidance rules play an important role to achieve this goal. But rules targeting tax avoidance cannot go against their purpose and treat some companies better than others,” the EU’s competition commissioner Margrethe Vestager said in a press release.

“This is why we will carefully look at an exemption to the U.K.’s anti–tax avoidance rules for certain transactions by multinationals,” she added.

The tax scheme in question is the Controlled Foreign Company rules that are meant to prevent U.K. companies from using a subsidiary in another country to avoid paying British taxes. The EU said the rules in general are “an effective and important feature,” but that the scheme since 2013 has included an exception for certain financing income of multinationals operating in the U.K.

Due to that exception, companies can avoid paying U.K. taxes on profits from certain transactions via their offshore subsidiaries.

The U.K. probe comes amid a renewed crackdown by EU tax authorities on its member states and big multinationals operating in Europe. Earlier in October, the commission ordered Luxembourg to recoup €250 million ($295 million) from Amazon.com Inc. AMZN, +4.71% in back taxes, saying the U.S. e-commerce giant received illegal state aid.

Vestager’s team is also investigating McDonald’s Corp.’s MCD, -0.19% tax affairs in Luxembourg, with a ruling expected later this year. In June, the commission slammed Alphabet’s Google GOOGL, +1.45% with a €2.42 billion fine for favoring its own comparison-shopping service in search results.