The letter has been jointly signed by Prakash Karat (CPM), S Sudhakar Reddy (CPI), Debabrata Biswas (Forward Bloc), Danish Ali (JD-S) and Abani Roy (RSP).
Amid the recent political turmoil within the UPA involving reports of strained relations between the Congress and the NCP, the timing of the SP chief's stridency on the FDI issue assumes significance.
In the letter, the leaders have expressed apprehension over the government's decision to revive plans to permit FDI in retail sector - the second largest employer in the country after agriculture.
"We urge the government not to open up the retail trade to FDI any further. Political parties across the spectrum are opposed to this move. Many state governments have also stated their opposition.
In the absence of a wide-ranging consensus, we request you not to proceed with this decision," Yadav and others have said in the letter.
The government had allowed FDI in single-brand retailing but had suspended the decision to allow such investment in multi-brand retailing due to opposition from several parties, including allies like Trinamool Congress.