The protest, which started at a centre near Rome on Saturday, came days after video emerged of immigrants at another camp standing naked in the cold to be sprayed for scabies. It drew new calls for the closure of detention centres and for changes to immigration laws.
Using a needle improvised from a cigarette lighter, four Tunisians each made a single stitch to join their lips in the middle, Filiberto Zaratti, a lawmaker who visited the protesters, said. Five Moroccans later imitated the gesture, according to the centre's manager, speaking on Italian television. The protesters asked to be let out of the centre, the manager said.
Italy has borne the brunt of a wave of immigration to the European Union, with more than 40,000 people risking the dangerous sea crossing from northern Africa this year - almost four times as many as last year.
Illegal immigrants can be held for up to 18 months awaiting deportation.
Despite stitching their lips, the protesters could still eat and drink and had been examined by a doctor, Mr Zaratti said, describing their conditions as shameful.