ROME (REUTERS) - Italian Prime Minister Matteo Renzi slammed trade unions on Friday after a temporary closure of Rome's Colosseum left hundreds of tourists stranded outside.

Unionised workers at the Roman amphitheatre held a two-and-a-half-hour meeting in the morning, keeping the gates locked until they had finished their discussions.

They said the stoppage was within their rights, but confusion reigned outside the Colosseum, with signs in English telling tourists that the site would not re-open until 11pm, rather than 11am.

"We will not allow anti-Italy unionists to take culture hostage," an angry Renzi wrote on Twitter, also publishing a photo of the crowds of tourists milling around outside the Colosseum.

The workers are locked in a dispute with the Culture Ministry over issues including staff shortages and payment delays. The Colosseum and the ancient city of Pompeii temporarily closed in July while unions discussed these issues.

Culture Minister Dario Franceschini said he would propose at a cabinet meeting on Friday that museums and cultural sites be included in a list of essential public services, which includes health and schools, and thereby restrict strike action.

Renzi appeared to respond to Franceschini's call, writing on Twitter: "Emergency law, today".

The CGIL, CISL FP and UILPA unions said in a joint statement that cultural heritage was already covered by legislation on essential services that deals with workers' rights and the needs of the public.

Despite coming from the centre-left of the political spectrum, Renzi has had a difficult relationship with Italy's unions during his 18 months in power.