Brazil’s archaeologists have lined up alongside conservationists and indigenous rights campaigners to protest against government proposals that they see as a threat to pre-colonial cultural heritage as well as forests, native communities and biodiversity.

The plan, to be debated by Congress on Wednesday, would roll back licensing rules for infrastructure projects, making it easier for construction companies to bulldoze sites of ancient Amazonian civilisations before they have been excavated.

Critics argue this is a new front in a battle for the country’s identity, since it could literally bury irreplaceable records of indigenous civilisations and reinforce the widely held but incorrect view that Brazil’s history began with settlement by Europeans.

“We draw upon the past to build our identity as a pluralist nation. This identity is now at risk, being sidelined by the image of a white and racist country,” archaeology lecturers from the Federal University of Western Pará wrote in a letter to congressmen.

Historians believe more than six million people lived in the Amazon forest before the arrival of predominantly Portuguese and Spanish explorers, gold miners and slavers, whose guns and viruses wiped out the vast majority of the native population over the following centuries.

Studies of pot fragments, black earth and contours of moats and walls suggest some of these communities were far more advanced than the later Victorian-era stereotype of “jungle savages” suggested.

Current laws oblige project consortiums to arrange surveys of possible new areas of historical interest, but this would be watered down – along with environmental protections and recognition of indigenous rights – under the government’s proposed reform. Instead, states and sometimes even companies would be able to establish their own procedures for licensing major projects.

The proposed change – launched in tandem with moves to soften demarcations of national parks, indigenous territory and ecological preservation areas – underscores the immense influence of the bancada ruralista (agribusiness lobby) in both Congress and the cabinet of the president, Michel Temer, who took power last year by helping to plot the impeachment of his former running mate Dilma Rousseff.

The government says the measures – some of which have been under discussion for 10 years – are necessary to trim bureaucracy, speed up project approval, help business and boost the economy.

However, 63 civil society organisations have also allied against the latest wave of efforts to open up more a million hectares of land for developers.

Brent Millikan of the International Rivers NGO said the moves would seriously undermine Brazil’s progressive legislation on human rights, environmental protection and heritage protection. “The end result of such attacks, which were are already beginning to witness, includes escalating land violence, destruction of forests and rivers and marginalisation of indigenous people and other local communities,” he said.

Socio-Environmental Institute, a Brazilian NGO, said the government’s plans represented the greatest regression in the country’s recent history and warned the impact on deforestation could undermine its commitment to the Paris Climate Agreement. Deforestation rates accelerated 29% last year.

The environment minister José Sarney Filho has also expressed alarm at the proposal, which he described as a major step back.