BRUSSELS (AP) — The European Union is going after Britain to see whether a special tax exemption for multinationals, which is part of a broader anti-tax avoidance plan, is legal.

The announcement of the in-depth investigation into the British scheme comes at a time of tortuous Brexit divorce negotiations between the EU and Britain.

EU Commissioner Margrethe Vestager said she wants to make sure that the British plan targeting tax avoidance does not allow some multinationals to pay less tax than other companies, which would be against EU rules.

She said that "rules targeting tax avoidance cannot go against their purpose and treat some companies better than others." The British plan came into force in 2013.