Both houses of Nigeria's National Assembly have passed a motion for President Umaru Yar'Adua, who is sick, to hand power to his deputy until he recovers.
Mr Yar'Adua has been in hospital in Saudi Arabia since last November.
The BBC reports his allies have been loathe to see Vice-President Goodluck Jonathan sworn in as acting president because of Nigeria's delicate regional balance of power.
Mr Yar'Adua is a northerner while Mr Jonathan is from the south.
The office of vice-president usually carries little weight.
But Mr Yar'Adua's absence has sparked legal challenges, cabinet splits and mass protests.
It has led to a freeze in government business and threatens progress made in halting unrest in the Niger Delta.
State governors decided last week to back Mr Jonathan to become acting president and have been lobbying senators ever since.
Separately, the Senate is also expected to consider a move to impeach the president.
Two weeks ago, the assembly asked Mr Yar'Adua to provide a letter confirming he was sick, which would pave the way for a formal transfer of power. But the BBC reports no letter has been received.