The Acropolis in Athens, one of the world’s most visited ancient monuments, has begun offering private visits for 5,000 euros ($5,400), setting off protests from the site’s guards.

According to the official website of the culture ministry unit that manages the hilltop site, these group visits will be held outside of normal opening hours and are limited to a maximum of five people each.

Normal visits cost 20 euros or 30 euros for a combined ticket with other sites.

“The Acropolis Experience now offers visitors the exclusive opportunity to enjoy this perfect architectural expression of the Greek spirit in private,” says the Hellenic Heritage website.

Up to four group visits can take place at a time, beginning at 7:00 am or 8:00 p.m. on Tuesdays, Fridays and Saturdays.

According to Greek media, the first such private visit took place on Saturday with a Russian couple and their private guide.

On Tuesday, the site was offering unguided visits starting July 12 and with guides starting August 2. The site says tours can be conducted in English, French, German, Greek, Portuguese, Russian and Spanish.

The program set off controversy when it was first announced last year, and the union that represents guards at archaeology sites said it opposes these private visits that by-pass the usual official guides.

“We were never given any information about how these visits are organized,” said the union’s president Georgia Kondyli.

Ranked as a UNESCO World Heritage Site and built in the fifth century BC, the Acropolis has attracted ever growing number of tourists, driven by cruise ship passengers.

The site received a record four million visitors last year or an increase of 31 percent from the previous year, forcing the organization that manages the country’s historic sites to institute timed visits.