In November, President Muhammadu Buhari appointed Onnoghen – the most senior justice of supreme court – as acting CJN following the retirement of Mahmoud Mohammed.
Since then, the presidency has not forwarded Onnoghen’s name to the senate for confirmation.
His three-month acting term will elapse on February 10.
In a statement on Thursday, Umar said the failure of the presidency to forward Onnoghen’s name to the senate for confirmation without any reason “leaves Nigerians guessing and speculating”.
“In a few days, the tenure of acting appointment of justice Onnoghen will expire. Going by our extant constitution, the acting CJN will be disqualified from appointment as the substantive CJN unless the NJC resubmit his nomination to the president,” Umar said in a statement.
“Already, many analysts view this action as a ploy to deny a southerner his right to succession based on his seniority in keeping with the appointment protocol observed the NJC in making the appointment.
“In the event of this occurrence, the NJC must not forward any other name nor should the senate confirm any other nominee.
“This will serve to check the excesses of this administration and reinforce the unity of the nation which has already been pushed to the precipice by the recruitment and appointment policies of a government which tends to favour the north in violation of the federal character provision of the constitution.”
On Tuesday, the Cross River caucus in the national assembly also asked Buhari to submit the name of Onnoghen to the senate for confirmation without “further delay”.