"There is a great risk that the law can prove dangerous for farmers," Mulayam Singh said.
"Wheat, rice and sugar are the biggest agricultural produce. If these are provided at low cost by the government, who will buy these from farmers? This is a major issue," the SP chief said.
He said that his party had received an assurance from the union government that the issue would be addressed.
The union cabinet has approved a food security ordinance, which aims to provide subsidized food grain to around 67 percent of India's 1.2 billion people.
The government, which is in minority and surviving on outside support, skipped a debate by passing the ordinance, inviting the ire of opposition parties who slammed the government for demeaning the parliament.
The Samajwadi Party, along with the Bahujan Samaj Party, are presently providing the government support from outside to have a majority in the Lok Sabha.