Work chains, (noun) work gangs ostensibly free but often 'conscripted' or 'drafted'. They are free labor but not slave. The chains are identified by color as depending on their purpose, such as 'black', 'red', or 'yellow'.
Ionicus was a master of work chains. He had several, the "red chain," the "green chain," "the yellow chain," and so on, each of which boasted several hundred men. Supposedly these were free work chains, "free" in the sense of not utilizing slaves.
Book 22, Dancer of Gor: Page 320