Farmers say they have been affected by falling prices and drought
A strike by Argentine farmers against an export tax on soya beans is into its fourth day - the seventh such stoppage in the past 12 months.
The farmers are angry over President Cristina Fernandez's refusal to lower the tax and her plans use the revenue for provinces and municipalities.
Argentina's farm sector has been hard hit by the global financial crisis.
The strikers say government aid has been spent on projects in cities at the expense of the countryside.
Farmers have set up checkpoints on more than 60 roads across the country.
Television pictures have been showing truckers carrying grain and livestock pleading to be allowed to pass the farmers road blocks.
In some places they were ordered to unload their cargoes of grain by the roadside so they could go on their way.
At the main beef market in Buenos Aires, the number of cattle on sale has been severely reduced.
Over the past year, the farmers have been trying to pressure the government to reduce the tax on exports of soya beans - the country's main crop.
They say they have been badly hit by the drop in global prices for commodities and because of a severe drought across the country.
The BBC South America correspondent Candace Piette, in Buenos Aires, says the strike is fuelling uncertainties about the abilities of President Fernandez's government to protect the Argentine economy.
Last week, Ms Fernandez's allies in Congress blocked a debate on a bill to lower the tax rate.
Her critics have been talking about a climate of hate now existing between farm leaders and President Fernandez.
Income from the taxes on cereals has become crucial for the government as the economy slows dramatically after six years of growth.
At a news conference last week, President Fernandez said the funding taken from soya exports would ease the impact of the global economic crisis and be invested in infrastructure projects throughout the country.
On the 18 March, the lower house of Congress approved a bill to bring forward legislative elections and the measure is expected to be passed by the Senate later this week.
President Fernandez has said it is important for the country to be focussed on economic issues rather than being distracted by months of political campaigning.
Opposition leaders have said the governing party is seeking to bring forward the elections before the economy worsens further.