Sen. Josh Hawley (R-MO) sent a letter to Apple CEO Tim Cook Tuesday, asking the executive to establish a “Do Not Track” option for Apple customers and make Apple an “industry leader” on technology privacy.

As Apple started its Worldwide Developers Conference (WWDC), Sen. Hawley asked Cook to create a Do Not Track option.

Sen. Hawley introduced legislation that would mirror this effort, the Do Not Track Act, which he co-authored with Sen. Dianne Feinstein (D-CA), which would create a system similar to the “Do Not Call” list, but for data tracking.

Hawley’s letter arises as the Donald Trump Department of Justice (DOJ) launched an antitrust investigation into Google, and the House Judiciary launched Monday a “top-to-bottom” investigation into antitrust issues in the technology industry.

Other senators such as Sen. Marsha Blackburn (R-TN) have sponsored the Browser Act, which would require the users “opt-in” into technology companies’ data mining, creating a simple way for users to protect their online privacy.

Hawley contended that the legislation would create a simple system to establish privacy for Apple users.

“The Do Not Track Act would prohibit any company from collecting any data beyond what is indispensable to its online services,” Hawley wrote. “All a person would need to do to obtain this protection is click a single button one time.”

The Missouri conservative’s letter follows as a report found that Apple’s App Store does not stop developers from hiding software in their apps designed to track users and harvest large quantities of data unrelated to the functionality of the app.

In the letter, Hawley cites Rovio, the developer of the game Angry Birds, which reportedly sends data through its apps to 43 different companies, at least three of which “almost certainly” violate the Children’s Online Privacy Protection Act (COPPA).

In his letter to Cook, Hawley writing that the chief executive of Apple has been highly critical of such practices, writing in one op-ed, “Let’s be clear: you never signed up for that.”

Hawley writes in his letter to Cook:

I am optimistic that Congress will give my bipartisan bill serious consideration, but you have the power to provide these protections to your customers even before Congress acts. If your company is serious about protecting privacy, you should give your customers the power to block all companies from collecting or sharing any data that is not indispensable to the companies’ online services.

Sen. Hawley concludes his letter by noting that Cook has a chance to “make good on [his] promise to be an industry leader” by implementing the privacy principles of the Do Not Track Act.

Read Hawley’s letter to Cook here.