The Customs boss asked the upper chamber of the National Assembly fix another date for his appearance.
Ali’s letter was read to lawmakers at the plenary on Tuesday.
The letter was signed by an Assistant Comptroller General.
The lawmakers condemned Ali for relegating the Senate and for failing to personally sign the letter.
President of the Senate, Sen. Bukola Saraki, after listening to the aggrieved lawmakers, said Ali must appear before the lawmakers on Wednesday and in uniform as requested by the legislature.