Singh and his former government have repeatedly denied accusations they cost the treasury billions of dollars in lost revenue by selling coalfields to private companies, without allowing competitive bidding.
The 82-year-old leader, who served as the nation's prime minister for two successive terms until last year, was not named as a defendant in the original dossier of charges, said Kanchan Prasad, the spokeswoman for the Central Bureau of Investigation (CBI).
Nevertheless, the trial court summoned him and some other corporate leaders to testify in person on April 8, she said.
The case Singh has been asked to appear for relates to the licensing of a coal block to a private firm some 10 years ago, when he was also guardian of the nation's coal ministry.
The summons has been issued under India's anti-corruption law.
Nothing to hide
Singh said he was open to legal scrutiny.
"(I) Am sure that the truth will prevail and I will get a chance to put forward my case with all the facts. I have always said I am open for legal scrutiny. Of course I am upset, but this is part of life," he said in a text message issued by his office.
Singh's Congress Party also came to his defense.
The former prime minister functioned with "utmost probity and utmost transparency" during his term, said senior Congress Party leader Manish Tiwari. He said Singh's legal team would thoroughly examine the summons, and indicated it may be challenged in a higher court.
Long political career
The Oxford-Cambridge educated Singh has been credited with ushering in economic reforms in India as its finance minister in the 1990s.
In his first term as prime minister, he initiated a historic nuclear deal with the United States that ended the South Asian nation's decades-old isolation in the global nuclear market.
His second tenure was hit by the unearthing of a series of scandals spread across various sectors.
In 2012, the national auditor alleged a widespread scam in the allocation of coal blocks.
Hunger for coal
India depends heavily on coal for power. The fuel is abundantly available in the country, but that's still not enough to satisfy the demand for energy in Asia's third-largest economy.
For the current financial year, national demand for thermal coal to produce energy has been estimated at 551.6 million tonnes, according to official figures. Of it, at least 84.7 million tonnes is being met through imports, coal minister Piyush Goyal told the Indian parliament in December.
The state-run monopoly Coal India Limited (CIL) accounts for more than 80% of the output.
Plans by current Prime Minister Narendra Modi for future privatization of the industry faced resistance recently, when CIL workers stopped work in January.
The two-day strike -- the biggest of its kind in four decades -- not only severely limited the ability of the companies to meet their production quotas, but forced the government to go slow on reforms.