Mr Singh is expected to reply to the court by the weekend India’s Supreme Court has directed PM Manmohan Singh to explain his “alleged inaction” in failing to sanction the prosecution of a former minister.
Telecommunications Minister A Raja has resigned over allegations he undersold mobile phone licences worth billions of dollars. He denies the claims.
Opposition MP Subramanian Swamy says he wrote letters to Mr Singh in 2008 calling for Mr Raja’s prosecution.
The court wants to know why Mr Singh remained silent over Mr Swamy’s plea.
It has now directed that Mr Singh should explain in writing his “alleged inaction and silence for 16 months” on Mr Swamy’s plea.
In India, the prosecution of a cabinet minister has to be cleared by the prime minister.
On Thursday, Solicitor General Gopal Subramaniam, who represented Mr Singh, told the court the prime minister had replied to all the letters written by Mr Swamy, an MP with the opposition Janata Party.
Mr Swamy has denied this, saying he had received only one reply from the prime minister this March, nearly 16 months after he wrote his first letter in November 2008.
“My only complaint is that Mr Singh sat on my letters,” said Mr Swamy. “He should have responded to it, one way or other.”
Mr Subramaniam told the court the prime minister had “maintained the highest tradition and propriety”.
“We have brought all the records and I be will be in a position to place before you the records. I only say that all the communication had been considered and dealt with,” he told the court.
The court asked the prime minister or any official on his behalf to submit a reply in writing by Saturday.
Federal auditors have said that rules were flouted in the 2008 sale of second-generation (2G) licences for mobile phones.
Licences in the lucrative market had been sold at “unbelievably low prices” – the loss to the government could be as high as $39bn (£24.3bn), the report said.
Mr Raja resigned over the weekend, denying any wrongdoing.
Correspondents say the row is one of India’s biggest corruption scandals in the Congress-led government’s six years in power.
Parliament has been adjourned in uproar after the government rejected a joint inquiry into the scandal.
While it has damaged the ruling party’s image, it is unlikely to threaten the government’s survival, correspondents say.
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