Last year the Italian government was accused of neglecting the Unesco World Heritage site near Naples in southern Italy when part of the "House of the Gladiators" fell down.
That collapse, along with three others in 2010, and the subsequent accusations of neglect and mismanagement, helped trigger a no-confidence vote against former culture minister Sandro Bondi in January.
Mr Bondi, a member of former Prime Minister Silvio Berlusconi's centre-right government, survived the vote but quit in March.
Officials said the latest part of the site to crumble was one of several columns that once held up wooden trellises in the house where Loreio Tiburtino, a Roman nobleman, lived.
Built in the second century BC, the house was renovated in 62AD, 17 years before the cataclysmic eruption.
"This is a torment without end," said Luisa Bossa, a lawmaker from the leftist opposition Democratic Party and former mayor of the Naples-area town of Herculaneum, also a major Roman-era archeological site.
"We have been complaining for three years but the country's most important archeological area continues to fall apart. The truth is that the site has been left alone for years and now, a bit at a time, we are paying the price," she said.
She called on Italy's culture minister, Lorenzo Ornaghi, to "take stock of the gravity of the situation and confront it with determination and speed".
Italy's archaeologists also voiced their concerns.
"To overcome the emergency created by these collapses, we need to hire specialised maintenance workers straight away. That is the only possible cure for Pompeii," Tsao Cevoli, head of the National Archaeologists Association, told news agency Ansa.
Pompeii was home to about 13,000 people when it was buried under ash, pumice pebbles and dust in 79AD as it endured the force of an eruption equivalent to 40 atom bombs.
Two-thirds of the 165-acre town has since been uncovered. Pompeii attracts some 2.5 million tourists each year, making it one of Italy's most popular attractions.