One of the world’s largest advertising firms is crafting a campaign to thwart a California bill intended to enhance people’s control over the data that companies collect on them.

According to emails obtained by POLITICO, the Interpublic Group is coordinating an effort against a bill that would make it easier for people to request that data brokers — firms that collect and sell personal information — delete their dossiers.

SB 362, known as the Delete Act, would require companies to delete all data on individuals upon request — including data purchased or acquired from third parties. This would shrink the trove of personal information they hold, such as browsing history, birthdates and past purchases. Data brokers compile this information to build profiles of people, which can be used to craft advertisements tailored to an individual’s preferences. But that also grants them access to some of people’s most sensitive details, such as whether they are pregnant or suffering from mental illness. The IPG emails reveal how an advertising company could use that same personal data and targeting capabilities to undermine a public policy proposal that threatens its bottom line.

The emails show an exchange between the company’s global chief digital responsibility and public policy officer, Sheila Colclasure, and other executives discussing what the firm can do to block the bill.

“We would like to mount an ‘opposition campaign’ using in-house digital advertising capabilities, targeting California,” Colclasure wrote in an Aug.14 email sent to others at IPG and reviewed by POLITICO.