Officers from the newly formed anti-slavery squad swooped on three addresses in Melton Mowbray, Loughborough and Bagworth.
Two men, aged 37 and 63, and two women, aged 36 and 64, were arrested on Thursday on suspicion of holding a person in slavery or servitude.
All four have been released on police bail while officers investigate.
Four people have been arrested on suspicion of slavery offences in raids across Leicestershire.