(Reuters) - Two consumer data brokers that sold information used to track individuals' religious and political beliefs, pregnancy status and more agreed to stop using data on visits to sensitive locations, the U.S. Federal Trade Commission said on Tuesday.

The FTC accused Mobilewalla and Gravy Analytics of engaging in unfair and deceptive practices by gathering location data without ensuring it had been obtained with the individuals' consent.

The settlements - including the first to bar gathering location data through online ad auctions - are part of the Biden administration's crackdown on data brokers over privacy concerns. The U.S. Consumer Financial Protection Bureau proposed rules on Tuesday to rein in the industry.

Websites, mobile devices and applications collect vast amounts of data on individuals which is sold and bought in secondary markets. While such data is typically used in online advertising, the FTC has expressed concern that it could facilitate stalking, blackmail, espionage and unlawful government surveillance.

Mobilewalla and Gravy Analytics used data showing the locations of mobile devices at certain points in time to sell products that could profile users based on visits to churches or political events, the agency said.

The companies agreed to stop using sensitive location data, and offer opt-out mechanisms for individuals.

Unacast, which owns Gravy Analytics, did not respond to a request for comment.

Mobilewalla in a statement disagreed with many of the FTC's allegations, but said the settlement will let it continue providing "valuable insights to businesses in a manner that respects and protects consumer privacy."

The FTC accused Mobilewalla of gathering location data on hundreds of millions of devices from online advertising auction platforms where companies bid for space to show their ads to specific audiences. It was the first time the FTC said that using such platforms to compile consumer location data is unlawful.

Mobilewalla agreed to stop gathering information from ad auctions for purposes other than bidding on ads.

FTC Chair Lina Khan said online ad auctions merit further attention from U.S. policymakers.

"The multi-billion-dollar industry built around targeted advertising may presently leave Americans' sensitive data extraordinarily exposed," she said.

Gravy Analytics sells location data to government contractors via its subsidiary, Venntel, raising constitutional concerns, Khan and her fellow Democratic commissioners said.

The FTC's two Republican commissioners, whom President-elect Donald Trump could tap to lead the agency after he takes office, partially supported the settlements.

Commissioner Melissa Holyoak agreed that selling location data to U.S. government agencies could violate individuals' constitutional rights.

Commissioner Andrew Ferguson took no position on the constitutional question, but said attendance at public protests cannot be considered sensitive information.