The development is also an indication that the anti-corruption chief, Fasih Bokhari, could be charged with contempt of court.
Chief Justice Iftikhar Chaudhry on Thursday issued a court order for Bokhari to appear before the tribunal on February 4 to explain the letter, which the official wrote earlier this week to President Asif Ali Zardari.
In the letter, Bokhari accused Supreme Court judges of trying to influence Pakistan's upcoming parliamentary elections.
Chaudhry said the letter amounted to interference in court matters and was an effort to incite against the judiciary.
If we don't react to this adequately, "people will lose confidence in the courts," he said, adding that the Supreme Court wanted to know why Bokhari went to such lengths as to write a letter to the president.
Chaudhry stressed that the top court fully backs the holding of free and fair elections, and that no one will be allowed to derail the democratic process.
Bokhari's clash with the judiciary stems from his refusal in mid-January to arrest Prime Minister Raja Pervaiz Ashraf over a corruption case involving kickbacks allegedly taken by the premier.
Bokhari refused to arrest Ashraf, citing lack of evidence.
The Supreme Court has repeatedly clashed with the government over the past few years.
The court last year convicted the prime minister's predecessor, Yousuf Raza Gilani, of contempt and ousted him from office for refusing to reopen an old corruption case against the president.