According to Socialisticheskaya Alternativa, there have been a lot of these kinds of open letters. In fact they are saying that a majority of people in Russia may be against the war.
"While people are getting angry, the regime is trying to stop discussion. Ten media outlets have been told to stop using the words “war” and “intervention” when covering Ukraine, or they will be shut down. Access to Facebook, Instagram, and Twitter are being restricted. The number arrested for participating in anti-war protests is now almost 3,000. But opposition to the war in Russia appears to be growing. Letters written by different groups, medical workers, teachers, students, IT workers, artistic workers are collecting thousands of signatures, while a general petition against the war has already been signed by a million people."
26 February 2022 | No to the war in Ukraine! Troops should return home. Build an anti-war movement in the workplaces and universities. This is the call being made by Socialisticheskaya Alternativa in Russia.
internationalsocialist.net