The inspection took place on Tuesday morning, with police and officials from the UK Home Office swooping on TK Nails on the High Street.
A spokesman for Police Scotland's Fife Division said: "Police in Fife conducted an intelligence-led welfare check on employees at a business premises on the High Street in Kirkcaldy on Tuesday 31st July, and enquiries are ongoing with partners."
A Home Office spokesperson confirmed that three men were found to be working illegally: "Immigration Enforcement officers supported Police Scotland during a visit to TK Nails, High Street, Kirkcaldy, at about 11am on Tuesday, 31 July.
"Three Vietnamese men, aged 19, 22 and 25, were found to be working illegally. All three were escorted from the premises and ordered to report to Immigration Enforcement regularly while their cases are progressed."