I'm talking of course of the common perception that Soviet soldiers who ran away or retreated from the Germans were shot by their own side for cowardice such as in movies like Enemy at the Gates.
It started a controversy in /r/jokes with several posters claiming that it simply wasn't true.
I must admit, I always just assumed it was true seeing how awfully genocidal Stalin's regime was, but when it comes to an enemy like the Nazis, I can imagine it would not take too much coercion to send soldiers into the fight.
As early as the first week of the GPW (Great Patriotic War) both Red Army fronts and NKVD troops were forming 'blocking detachments' to counter unauthorized withdrawals; These consisted of 'reliable fighters' of between battalion and company size positioned directly behind the front.
In one 24 hour period during the battle for Stalingrad Beria boasted that the blocking detachments of 62nd and 64th armies detained 659 people, shot 7 'cowards' and one 'enemy of the people' in front of the troops, with another 24 being arrested: one 'spy'; 3 'betrayers of the motherland'; 8 cowards; 4 deserters and 8 'enemies of the people'. During its epic resistance in Stalingrad the 10th NKVD division arrested and processed 63,547 people, including 1,146 soldiers who had surrendered, deserted, or escaped from encirclement.
Yes, it happened. Often. Those who weren't summarily executed usually were assigned to a Shtrafbat, or penal battalion, to which hundreds of thousands of Red Army soldiers were consigned throughout the course of the war.
There's a lot of people who like to try to refute this and totally hate when it's brought up during the topic, but Order 227. Basically it meant that Soviet soldiers could be killed during combat if they were found to be cowardly and/or lower morale of the troops.