A union meeting kept Rome's 2,000 year-old Colosseum, the Roman Forum and other major archaeological sites closed on Friday, sparking the ire of Italy's culture minister Dario Franceschini.
"This is too much. It's got to stop," Franceschini said.
Queues of confused tourists formed at the sites, which also included the Palatine Hill and Baths of Diocletian, and the ancient Roman city of Ostia Antica, outside Rome, which were due to open when the union meeting finished at around 11.30 am.
"Unfortunately, there is no network to inform tourists," said Francesco Prosperetti, superintendent for Rome’s Archaeological Heritage.
"We are talking about a legitimate union meeting and not a strike. Under law, such meetings do not have to be authorised and only require the employer to be informed three days in advance."
A meeting of Italy's cabinet was due later on Friday to discuss premier Matteo Renzi's proposal to put museums and monuments on a list of essential public services, a plan backed by Franceschini.
In July, a union meeting closed the Pompeii near Naples, as long lines of irate tourists waited for hours in searing temperatures for the UNESCO Word Heritage site to open.
The site of Pompeii closed to visitors angered the government and drew criticism from largest trade union federation CGIL.
