A21-year-old Indigenous activist from a remote Amazonian village will hand deliver a letter to the Cargill-MacMillan dynasty in Minneapolis on Thursday, calling on the billionaire owners of America’s biggest private company to stop destroying the Amazon rainforest and its people.

Beka Saw Munduruku traveled more than 4,000 miles to confront the family behind Cargill, the world’s largest grain trader and a major meat producer, over what she says amounts to a litany of broken promises that pose an existential threat to Indigenous peoples and the global climate.

“Your executives tell us that Cargill is a good company, that they have pledged to end the destruction of nature. But this is not our experience. In every region where Cargill operates, you are destroying the environment and driving out or threatening the communities who live there,” writes Beka, whose requests for face-to-face meetings with family representatives went unanswered.

“Despite your many commitments to end deforestation, the destruction has increased … We have lived here in the heart of the Amazon for over 4,000 years. But now our world hangs by a thread.”

Beka is part of the Munduruku community of 13,000 people who live in 160 communities across three states in northern Brazil. “We are known as the Red Ants for our determined resistance and protection of our territory,” she told the Guardian in New York – en route to Minneapolis.

Beka’s visit to the US is part of a campaign by Stand.Earth, a non-profit environmental watchdog with more than a million members globally, to pressure the Cargill-MacMillan clan to take responsibility for their company’s harms. Numerous investigations have found that Cargill’s grain supply chain continues to be linked to human rights abuses and deforestation in the Amazon forest and Cerrado savannah, despite the company’s promises to eradicate harmful practices.

Cargill has promised to be “deforestation-free” in the Amazon and Cerrado by 2025 and completely eradicate deforestation from all its supply chains by 2030. The company has previously said that it has put in place a sophisticated monitoring operation at ports, warehouses and other points in its supply chain.

“I understand that many others have denounced Cargill over the years, but the company has never changed. I believe it’s important that young people bring a message to the Cargill family. We want our people to be heard and consulted,” Beka said. We want them to look at us and respect us and hear our call. Sending letters isn’t enough, we need to show up and be present to be heard. This is personal.”

The family is the fourth richest in the US, with an estimated net worth of $47bn, according to Forbes.

Beka was 12-years old when she first helped her father, a village chief, in a campaign to stop construction of a hydroelectric dam threatening to flood Munduruku and other Indigenous lands. Since then she has witnessed her village on the Tapajos River, in the state of Pará, battle mercury poisoning from illegal gold mining, deforestation by illegal loggers and diseases linked to agrotoxins and industrialized diets like diabetes and some cancers as communities have been denied access to their land, water and traditional food sources.

Cargill stands out among the companies damaging the Amazon and its people, according to Beka.

“Cargill is one of the main companies occupying our sacred lands to make money. Cargill is driving deforestation, and pressuring Indigenous people to leave as they can no longer fish and hunt which is the source of our food security, customs and wellbeing …. Expanding soy on our lands leads to deforestation and global warming that affects everyone.”

The Cargill empire started as a grain storage facility in 1865, and continues to be owned by descendants of the founder William Cargill and his son-in-law John MacMillan. Family members own around 88% of the conglomerate – which reported $165bn in revenues last year – that produces, distributes and trades in beef, turkey, palm oil, grains, sugar, chocolate and pet food among other agricultural, food, beauty and financial products and services.

“While not necessarily engaged in the day-to-day business of the company, as its owners these individuals have the ultimate say over – and the ultimate responsibility for – Cargill’s practices,” said Mathew Jacobson, Stand.Earth’s campaign director.

The latest threat facing Beka’s people and the region comes from a 620-mile railroad backed by Cargill known as Ferrogrão, that would transport soya grown in Cerrado – a critical savanna ecosystem just south of the Amazon where communities already face land grabs from ranchers and contamination of their waterways and fish from pesticides.

The railroad would bring additional transport capacity to the soy highway that currently connects the Cerrado to the Miritituba port in Pará, and could impact six Indigenous territories and three isolated tribes. Studies have found it would likely bring a slew of socio-economic harms to Indigenous peoples, encouraging soy and other commodity production that drive deforestation, and lead to tens of millions of tons of additional carbon emissions.

In her letter, Beka lays out the potential devastating consequences to the family.

“Last year the forests and savannas of the Cerrado were destroyed at a rate of 8,000 acres a day … an area the size of your hometown of Minneapolis every five days. This railway will destroy 2,000 square kilometers of the Amazon forests we live in …it will open our lands to more land grabbers and illegal miners and loggers that already invade and burn our lands and murder our people.”

The Brazilian supreme court suspended the Ferrogrão in 2021, but recently opened the door for a revised plan before a final vote.

Cargill has previously said that Brazil needs to continue investing in commodities infrastructure and that anyone opposing the Ferrogrão is “irresponsible”.

Beka said: “The Ferrogrão railroad will bring a package of death and destruction to our territory and people.

“We are fighting for our lives. For our land. For our cultures. For our children and grandchildren. This is not irresponsible … You have the power to stop this.”

“Beka traveled all the way from her remote Amazonian village to bring a message directly to the Cargill-MacMillan family because her people have been forced to endure Cargill’s destructive practices and broken promises firsthand and without recourse. The Munduruku are demanding that the family rein in the company’s reckless conduct,” said Paula Vargas, Amazon Watch Brazil program director.

The spotlight on the family, which includes 12 billionaires, comes as Cargill is facing legal scrutiny on multiple fronts in relation to allegations of land grabs and broken promises on deforestation and Indigenous rights. In Brazil, federal prosecutors are investigating the American company and a local partner for alleged irregularities in land acquisitions in Abaetetuba, a coastal city in Pará, where the company wants to build a massive grain export terminal. In the US, the company is facing a legal challenge over its alleged failure to remove deforestation and human rights abuses from its soy supply chain in Brazil.

Cargill did not respond to the allegations made in Beka’s letter but earlier this year in response to the US legal case told the Guardian that it had an “unwavering commitment” to eliminate deforestation and conversion in South America. In line with this, it added: “We do not source soy from farmers who clear land in protected areas and have controls in place to prevent non-compliant product from entering our supply chains. If we find any violations of our policies, we take immediate action in accordance with our grievance process.”

Beka is now a spokesperson for the Mundurukus, and alongside Alessandra Korap Munduruku, who earlier this year was awarded the prestigious Goldman environmental prize for leading efforts to stop a British mining company encroaching on Indigenous lands, is part of a new generation of female Amazonian leaders demanding accountability.

Beka said: “The people here who want to protect the Amazon need to look past the forest and see its peoples. Deforestation is linked to the blood of Indigenous people that is spilled in defending the lands that you are concerned about. People here are eating comfortably while we cannot eat our traditional foods as a result of these products. I consider this to be a great disrespect to our people.”