The UNSA and FLP labour unions, representing employees of the site's Special Superintendency, had asked for authorization to hold a demonstration in front of the entrances to Pompeii, according to Le Cronache della Campania.
But the protest, planned for Thursday, coincided with a planned visit to the site by Italy's Culture Minister Dario Franceschini and European Commissioner Corina Cretu, and is now not allowed to take place.
Police said the reason for banning the protest was to "protect public order", and that carrying out the demonstration in spite of this decision would be a criminal offence.
Instead, workers will be allowed to gather in front of the Porta Marina inferiore gate - the entrance which will be used by members of the media attending Thursday's press conference.
A regional councillor from the Green Party, Francesco Emilio Borrelli, said he had been organizing a counter demonstration to show support for Pompei's superintendency.
"Three hundred people had already said they would join, to show that the trade union protest was specious and that the people of Campania did not agree," Borrelli told Il Gazzettino Vesuviano. After the ban on the union protest, the counter demonstration will not take place either.
There have been ongoing disputes between workers at Italy's heritage site and the Ministry of Culture, both over pay and working conditions, and the way in which work is carried out at the fragile ruins.
Back in 2013, many of Italy's sites, including Pompeii and the Rome Pantheon, were shut down over a pay row amid claims that some workers had not been paid for months.
The following year, experts told The Local that Pompeii was being put at risk by red tape. Problems raised included companies cutting corners to win bids on restoration work, bureaucratic hurdles, and pay delays.
And in November 2015, Italy passed a law aimed at cracking down on strikes at its prized ruins. The emergency decree reclassified the country's historical sites as essential services, therefore making it harder for workers to strike.
The move, dubbed the 'Colosseum' decree, followed two unannounced strikes by workers at the Rome monument and in Pompeii.