By Tom Gibb
BBC correspondent in Sao Paulo
Several hundred peasant activists have occupied a research farm in southern Brazil owned by a Swiss multinational biotechnology company.
Peasants accuse the Swiss firm of sowing GM seeds
The Landless Movement says the move is part of a new strategy to target multinational agribusiness, which it accuses of pushing farmers off land.
It also says such companies are destroying the environment.
The Landless Movement has also occupied dozens of farms and cattle ranches to press for land reform.
At least 300 peasants from the Landless Movement took over the experimental farm belonging to the Swiss company Syngenta, accusing it of sowing genetically modified seeds close to a nature reserve.
About one million seedlings were destroyed last week
The company denies breaking environmental rules.
The Landless Movement has long occupied farms to demand land reform from the government, which is the aim of most of the dozens of farm takeovers over the last week.
But leaders of the Landless Movement say they will now also target big agricultural companies in alliance with the international peasant movement, Via Campesina.
It is the second such protest in less than a week.
Last week about 1,000 women from the movement took over a tree nursery in southern Brazil, destroying around one million eucalyptus seedlings.
Brazilian government officials - who have been supportive of the Landless Movement in the past - strongly criticised the destruction.
The country's economic growth is dependent on agricultural exports, many of them channelled through multinational companies.