By Leslie Gevirtz

NEW YORK (Reuters) - Financial news and data firm Bloomberg LP, founded by New York City Mayor Michael Bloomberg, is facing a lawsuit involving 58 women who say they had their pay cut, were demoted or denied opportunities because they had become pregnant.

The U.S. Equal Employment Opportunity Commission, which filed the lawsuit, said on Thursday the number of claimants had risen from three since September and could rise further.

EEOC attorney Raechel Adams told a pre-trial hearing in the U.S. District Court for the Southern District of New York that her agency had sent questionnaires to 478 women who were at Bloomberg LP and had taken maternity leave since 2002.

Michael Bloomberg, who became mayor in January 2002, retains a majority stake in the company but has said he has given up day-to-day control.

The cases go back to February 2002.

Adams said the EEOC was still conducting follow up interviews with the women, not all of whom are in the United States. "It is a global action," Adams told Reuters.

The lawsuit also claims the women were paid less when they returned from maternity leave and were demoted and replaced by "junior" male employees.

The EEOC took action after Jill Patricot, Tanys Lancaster and Janet Loures filed charges with the government agency.