"Senior Russian military leaders recently had conversations to discuss when and how Moscow might use a tactical nuclear weapon in Ukraine", multiple senior US officials tell the NYT.

https://www.nytimes.com/2022/11/02/us/politics/russia-ukraine-nuclear-weapons.html

Russian Military Leaders Discussed Use of Nuclear Weapons, US Officials Say

The conversations alarmed the Biden administration because they showed how frustrated Moscow had become over its battlefield setbacks in Ukraine.

The New York Times