By Foo Yun Chee

BRUSSELS The European Commission stuck to its guns on Friday, saying it was not reconsidering EU antitrust chief Margrethe Vestager's pick of a U.S. economist to a senior job helping to oversee Big Tech despite criticism from French ministers and EU lawmakers.

Fiona Scott Morton, 56, the former chief economist at the U.S. Department of Justice during former President Barack Obama's tenure, will take up her three-year stint on Sept. 1 when the current chief economist, Pierre Regibeau, retires.

She will be the first non-EU national, first U.S. national and first woman for the job.

The leaders of the four main political parties at the European Parliament on Friday wrote to Vestager asking her to reconsider her decision, echoing calls from two French ministers a day earlier.

They cited the strategic importance of the post, potential conflicts of interest due to Scott Morton's previous work with Big Tech, and her previous public antitrust comments.

Commission spokeswoman Dana Spinant brushed aside the criticism.

"The college endorsed the proposal to appoint this person to the position. The decision was made. We see no grounds to reconsider," she told a daily press conference.

Head of the centre-right group European People's Party Manfred Weber, president of the liberals' group Renew Europe Stephane Sejourne, head of the socialists group Iratxe Garcia Perez and the heads of the green party Philippe Lamberts and Terry Reintke said they opposed the new hire.

To avoid conflicts of interest, Scott Morton will not work on cases in which she has previously been involved, or on cases involving companies for which she had worked for previously as a consultant.

(This story has been corrected to change the quote to read 'no grounds' instead of 'no wrong', in paragraph 7)

(Reporting by Foo Yun Chee; Editing by Jan Harvey)