BRUSSELS (AP) — The European Union's anti-trust watchdog has opened an investigation into U.S. oilfield service provider Halliburton's planned merger with rival Baker Hughes.

The European Commission, which oversees competition issues in Europe, said in a statement on Tuesday that its probe would assess whether the move "would impede effective competition in breach of the EU merger regulation."

The merger has also drawn the attention of U.S. federal regulators, and the companies had been divesting assets to win approval for the deal.

The takeover would unite the world's second- and third-largest oilfield service suppliers against market leader Schlumberger.

EU Competition Commissioner Margrethe Vestager said the commission must ensure that any merger "would not reduce choice or push up prices for oil and gas exploration and production services in the EU."