Police investigating forced labour allegations arrested three men at a car wash in Louth.
All three men, aged 19, 27 and 49, from the Grimsby area, were arrested on suspicion of modern-day slavery offences and are currently in police custody.
The police arrested the men at the New Hand Car Wash on the Fairfield industrial estate in Louth.
Officers also want to speak to anyone who witnessed a possible assault of one of the workers in the last three weeks.
They believe a taxi driver may be among the witnesses who could help.
Anyone with information which could assist the investigation has been urged to call 101 and quote incident 144 of January 11.