EU's competition chief Margrethe Vestager under fire for hiring a U.S. economist

Europe's powerful competition chief, Margrethe Vestager, is under fire for hiring an American citizen for one of her team's top jobs.

Vestager, who's been leading investigations into Big Tech for almost 10 years, is due to answer questions from European lawmakers Tuesday after appointing Fiona Scott Morton, a professor at the Yale School of Management, as chief competition economist at the European Commission, the EU's executive arm.

The heaviest criticism has come from French government members. Laurence Boone, France's secretary for Europe, said on Twitter that she had spoken with Vestager about this nomination, adding that "Europe has many talented economists."

"We have engaged, without a delay, in a dialogue with the commission so that the appointments are consistent with our European ambitions," she said.

Jean-Noël Barrot, France's minister delegate in charge of the digital transition and telecommunications, also said via Twitter, "At a time when Europe is embarking on the most ambitious digital regulation in the world, the recent appointment of the chief economist of the DG [directorates-general] Competition is not without raising legitimate questions."

"I invite the European Commission to reconsider its choice," he added.

When contacted by CNBC, a spokesperson for the commission highlighted previous comments where the Brussels institution announced her appointment, "With a distinguished academic background and decades of experience in economic analysis and competition policy, Fiona Scott Morton possesses a deep understanding of market dynamics and regulatory frameworks."

"Her track record in advising governmental agencies highlights her ability to provide strategic and informed guidance on complex economic issues, making her highly suitable to advise on the economic aspects relating to the policy development and enforcement of competition rules in the EU."

Scott Morton has a bachelor`s degree from Yale College and a Ph.D. in economics from the Massachusetts Institute of Technology. She also worked in economic analysis at the antitrust division of the U.S. Department of Justice between May 2011 and December 2012. However, one of the biggest issues raised has been her experience in consulting for Big Tech.

A group of European lawmakers wrote a letter to Vestager last week saying they "learnt with dismay" about the appointment.

"We are very concerned about the opposite views she publicly expressed and the potential conflict of interests between her new role and her previous functions with large American tech companies," they said in the letter, shared by one lawmaker on Twitter.

A spokesperson for the commission previously explained that the there was "a limited number of applications." Scott Morton is set to start the new role in September.

Correction: The European Commission is the EU's executive arm. An earlier version misstated its status.