Rule 6(e)
The most famous example of invoking it came in the Watergate investigation, when federal courts allowed the special prosecutor's office to see grand jury information because Congress had authorized the Judiciary Committee to open a formal impeachment probe.
https://www.dailymail.co.uk/news/article-6989785/Trump-opponent-Jerry-Nadler-demands-Bill-Barr-Democrats-Mueller-report.html