Facebook quietly pushed out changes to News Feed that’s “interfering” with the browser-based tools used by journalists and researchers, according to The Markup, the nonprofit news organization behind Citizen Browser.

According to the report, Facebook has been adding “junk code to HTML features meant to improve accessibility for visually impaired users.” The resulting code prevents browsers from automatically collecting data about posts in News Feed, and may also be hindering screen readers used by blind and visually impaired users.

The change has affected both The Markup’s Citizen Browser, as well as New York University’s Ad Observer, a browser extension that has helped researchers study political ads and vaccine misinformation. These types of browser-based tools have become increasingly important to researchers trying to study issues like ad targeting and misinformation. Researchers say these tools, which allow users to make the posts from their feeds available to academics and journalists, is one of the only ways to access important data about how News Feed works.

Laura Edelson, lead researcher at NYU’s Cybersecurity for Democracy, which runs Ad Observer, said Facebook’s changes “had the effect of breaking Ad Observer” though they were able to find a workaround.

In a statement, a Facebook spokesperson said that the company was “investigating” the claims. “We constantly make code changes across our services, but we did not make recent code changes to block these research projects,” the spokesperson said. “Our accessibility features largely appear to be working as normal, however, we are investigating the claimed disruptions.”

The code change is the latest dustup between Facebook and researchers who say Facebook has hindered their efforts to understand what’s happening on its platform. Last month, the company disabled the personal Facebook accounts of NYU researchers working with Ad Observer saying they broke the company’s privacy rules. (The FTC later rebuked Facebook for making “misleading” comments about its reasons for taking these actions.)

There are other implications to the changes. As The Markup and Edelson point out, the changes could affect screen readers, an important accessibility technology. They cite at least one instance of the code appearing to cause a screen reader to read out some of these “junk” characters. The changes may have also contributed to problems with some ad blockers.