Paraguay's Congress has approved a 10% tax on exports of grain, wheat, corn and sunflower seeds.
The tax is designed to ease the country's fiscal woes and promote grain processing at home. The government hopes to raise $300 million a year from the tax.
Producers oppose the plan, claiming it will hurt competitiveness.
Soybean farming in Paraguay has been growing quickly over recent years amid heavy investments from Brazilians along the border.
Major soybean trading and processing firms, including ADM, Bunge, Cargill, Louis Dreyfus Commodities and Noble have operations in Paraguay.