Forced labor is when labor is done involuntarily, under the threat of penalty. That would be what the working class is subjected to under capitalism. You must work for your capitalist overlords to give you enough for basic subsistence. Don't work, face the repercussions of poverty, even though we already produce enough to feed you.
The USSR never fully achieved communism, even by its own admission. So they still operated under a capitalist mode of production with respect to the global economy. So people were also required to work, but there were many improvements. Worker conditions and rights we're far better in the USSR. The USSR had the "right to work" policy, meaning as long as you are willing to work, you're fine, even if it means sitting in an office doing little. The USSR also operated the means of production in a centralized manner towards bettering its society and reducing working hours.
You called it "directed labor". Not sure what you mean by this, but you later called it "slavery". I suppose you could call it wage slavery, as it still operated in surplus production, but it was an improvement on capitalism and towards achieving communism. People were working for their own interests and needs, not for capitalist profits.