Members of Brazil's Landless Workers Movement (MST) have occupied 12 farms to try to pressure the government to speed up land reform.
Campaigners say they are occupying only disused land
More than 5,000 families from the MST have moved on to the farms in the north-eastern state of Pernambuco, one of Brazil's poorest.
The MST said the government had failed to live up to its election promises to have settled 400,000 families by 2007.
The government says it has settled little over a quarter of that number.
The MST said the real figure is much lower.
Brazil has one of the biggest wealth gaps in the world. Nearly half of all farmland is owned by just 1% of the population.
Brazil's Landless Movement, the MST, usually steps up action in April to commemorate the murders of 19 activists in 1996.
MST leaders said they still had hope in Brazil's first working-class president, Luiz Inacio Lula da Silva, who promised to buy disused land and redistribute it to poor families with no home of their own.
"We still believe in Lula; it's his economic team which is neo-liberal," Joao Paulo Rodrigues, a national coordinator for the MST, told the Reuters news agency.
"The government has to make a radical change in its land reform policy. Next year there are elections so Lula has to do it now."
The MST has said it has occupied only unused land.
However, it is angry the government has prioritised debt payments and cut the land reform budget.