The blockade is a part of a series of protests to demand the company's re-nationalization.
The Landless Workers' Movement also said 3.6 million people voted for the return of CVRD to state hands in last month's informal, nonbinding vote organized by it and other groups.
A spokeswoman for the group said earlier this month the blockades of railroad tracks was "part of a series of actions of the nationwide movement to annul the company's privatization."
Unions and social rights groups that promoted the CVRD plebiscite last month in 4,000 Brazilian municipalities say the CVRD privatization was fraudulent.
The control of CVRD, which had been profitable as a state-owned company since its foundation in 1942, was sold in auction in May 1997 for 3.3 billion reais (at that time worth about $3.3 billion).
The organizers of the plebiscite argue that CVRD's market value at the time was in tens of billions of dollars. CVRD is now worth around $150 billion and its second-quarter net profit alone was $4.09 billion.
Brazilian President Luiz Inacio Lula da Silva has ruled out the re-nationalization, even though his ruling Workers' Party backed the plebiscite.
The following is from the International Herald Tribune.
Landless activists block railway owned by Brazilian mining giant CVRD
Landless activists blocked a key iron ore export railway for global miner CVRD on Wednesday, demanding the company fund social programs and give activists a say in decision-making.
It was the third time in less than a month that protesters from the Landless Workers Movement, or MST, invaded the railway to block CVRD's shipments, the company and authorities said.
Companhia Vale do Rio Doce SA, the world's largest iron ore miner, uses the railway at the Carajas mining complex to transport 250,000 metric tons (275,600 tons) of iron ore daily from its sprawling Amazon mine to Atlantic ports for shipment overseas.
CVRD said the iron ore — the key ingredient in making steel — transported daily on the railway is worth US$11.2 million (€7.6 million).
The company said the blockade is also keeping 1,300 passengers from using the railway and stalling fuel shipments to small cities in rural Para state.
CVRD said in a statement that about 300 MST members — some of them armed — surrounded two trains near the northern city of Paraupebas and cut brake lines. It said four workers and a train operator were held for about half an hour, then released.
There were no reports of injuries.
The MST said 6,000 people invaded the railway, which cuts through a camp of about 520 MST-affiliated families. Police numbered the protesters at fewer than 500.
"We want to put land reform and the management of our natural resources at the center of the political debate" in Para, said Ulisses Manacas, coordinator for MST and the peasants rights group Via Campesina in the northern Amazon state, in a prepared statement.
The activists also demanded CVRD invest in local educational and health programs and allow more public participation in company decisions.
CVRD was previously owned by Brazil's government but went private in the 1990s. Activists and left-wing politicians have recently being lobbying for the state to retake control of CVRD and other formerly state-owned companies.
Soaring iron ore prices have meant record profits at CVRD. The company recently posted third-quarter profits of US$2.6 billion (€1.8 billion).
CVRD has invested heavily to boost production at its Carajas mining complex, but the railway that carries its ore to the Atlantic has been periodically shut down by protesters seeking concessions from CVRD and Brazil's government.
CVRD's U.S. traded shares were down 3.2 percent at US$36.56 (€24.83) on the New York Stock Exchange on Wednesday.