A privacy advocacy group has filed a formal legal complaint with the United States Federal Trade Commission (FTC) to request an investigation into Google’s potentially invasive practice of tracking in-store purchases made by consumers.

The filing, made by the Electronic Privacy Information Center (EPIC), raises concerns regarding Google’s Store Sales Management program which allows the search giant to track customer behavior and financial data through offline purchases.

Read: Google-EU Antitrust Case: Search Giant Expected To Be Hit With Record Fine

Google’s program, which debuted in May, gathers consumer data collected by data brokers and through financial transactions and creates a uniform profile that can be used by businesses to see how searches online translate to sales in store.

The details of how Google’s algorithmic profile creation system works remains under wraps, which EPIC has taken issue with. While Google claims to anonymize all data—making sure that names, credit card numbers, location and other private data cannot be used to identify an individual—there is no way to confirm the company is actually honoring the promise of anonymity.

At issue in particular for EPIC is Google’s use of CryptDB, an encryption protocol designed to allow users to search through a database of information without revealing the full contents. CrtyptDB has come into question in the past for being vulnerable to exploits.

In 2015, a team of researchers at Microsoft were able to successfully exploit vulnerabilities in the algorithm. The researchers targeted a database of medical records and we able to access large portions of sensitive patient data.

Read: Why Was Google Fined $2.7 Billion?

EPIC also raised the concern that consumers do not have a clear opt-out ability to make sure their data is not included in Google’s program should they want to avoid it.

"Consumers cannot easily avoid Google’s tracking of their in-store purchase behavior," EPIC’s complaint states. "There appears to be no mechanism by which Google users can opt out of purchase tracking other than by disabling location tracking entirely. It is not clear to users, however, that the way to avoid tracking of purchases is by disabling location tracking."

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It’s worth noting that it is possible to opt out of this tracking, though EPIC believes the option to do so does not go far enough to guarantee the privacy of a user. “ "There does not appear to be a way to prevent Google from matching user data to credit card transaction data held by a third party," the advocacy group said.

In order to disable the tracking, Google users can go into their account, visit the My Activity page, click on Activity Controls on the menu to the left and turn off the "Web and Web Activity" option—and any other options that you may not want to participate in.

The challenge is just the latest to Google’s practices when it comes to its shopping-related practices. Earlier this year, the company was hit with a $2.7 billion fine by the European Union for what the governing body determined to be providing favorable treatment to paid advertisers and sponsored search results.