India's Supreme Court has directed the country's top detective agency to investigate the sources of wealth of a leading politician.
Mr Yadav is the head of the regional Samajwadi Party
The court asked the Central Bureau of Investigation (CBI) to probe the assets of chief minister of northern Uttar Pradesh state, Mulayam Singh Yadav.
Mr Yadav's Samajwadi Party said the case was "politically motivated".
The petition alleges that Mr Yadav and his sons had amassed millions of rupees since 1977.
The court also asked the CBI to investigate the sources of wealth of the sons, Akhilesh and Prateek.
The court gave the order against Mr Yadav on a petition filed by a lawyer.
The General Secretary of the Samajwadi Party, Amar Singh, accused the petitioner, Vishwanath Chaturvedi, of having links with the Congress party.
He cast doubts on Mr Chaturvedi's credibility, accusing him of accepting that he was a Congress party worker before the case, but later denying it in court.
Uttar Pradesh is India's most populous state, with 80 MPs in the federal parliament.
Assembly elections in this politically crucial state are due in April and May.