MEXICO CITY — Mexicans are taught to revere their pre-Columbian roots. So some archaeologists are outraged by what they view as the government’s failure to safeguard the nation’s Mayan palaces and Aztec pyramids.

A recent decision by the government to erect a glass-and-steel facade on a portion of the historic Fort of Guadalupe in Puebla in time for the Sept. 15 Mexican independence celebrations was the last straw. The archaeologists have occupied Mexico’s prestigious National Museum of Anthropology, telling visitors that taking liberties with federally protected buildings was becoming commonplace.

The late-summer tourists who flock to the Chapultepec Park institution are greeted by banners, petitions and angry anthropologists with megaphones. A barefoot Mayan-speaking researcher in a white tunic blows into a conch shell to announce speeches in the lobby.

The occupying scientists have also declared: Admission is free.

Archaeologists are tweeting about “aggressions against patrimony” and using Facebook to decry tacky tourist development and New Age spectacles that they say will ruin the ruins.

Just when government officials were hoping to make money on the hype over Dec. 21 marking the end of the world, as predicted by the Mayan calendar, archaeologists are threatening to shut down the party even before it has begun.

“Our national monuments are being violated,” said Felipe Echenique March, head of the union that represents the National Institute of Anthropology and History (INAH), the government agency charged with protecting historic sites. “Public archaeological sites are deteriorating. We are resisting this destruction.”

Authorities were largely silent until last week, when the agency’s archaeological council said in a communique that it “categorically denied the claims of union groups pursuing political aims.”

Echenique said authorities called him into the attorney general’s office Thursday and accused him of depriving the National Museum of Anthropology of more than $400,000 in revenue since the protest began late last month. Spokesmen for the attorney general’s office said they were unaware of the conversation.

“We do have a political aim,” Echenique said. “We want enforcement of the federal laws that protect patrimony.”

In recent days, protest banners have spread to sites such as the former palace home of Spanish conqueror Hernan Cortes in Cuernavaca and a church in Nuevo Leon, aimed at what one bulletin called “the enemy in the house” — ineffectual leaders of the INAH.

Archaeologists have come from Michoacan to protest the ongoing construction of a museum on a pre-Columbian base at the complex of circular pyramids at Tzintzuntzan, or “place of the hummingbirds,” the capital of the Tarascan people until the Spanish conquest.

“They should not build this in an archeological zone. There might be important tombs below,” said Celia Gutierrez Ibarra, a 33-year state historian and author who stopped by to sign a petition calling for the protection of historic monuments.