Abuja - The leader of Nigeria's upper chamber of parliament on Tuesday blocked 11 lawmakers from defecting, saying their break from the ruling party to the main opposition would not go through until a court challenge was resolved.
Senate leader David Mark, a heavyweight in President Goodluck Jonathan's Peoples Democratic Party (PDP), has been lobbying the group to reverse its decision to defect announced in a letter on January 29.
Jonathan has suffered a string of recent political blows, including a mass defection of lower house lawmakers to the All Progressives Congress (APC) that stripped its parliamentary majority.
The PDP has challenged the Senate defections in a federal court by seeking to have the seats declared vacant on the grounds that party-switches violate the will of voters.
"The matter is in court and therefore we can make no reference to it," Mark said, interrupting one of the would-be defectors, who sought to formally cross the floor.
The rest of the group then stood to have their defection officially recognised but were shouted down by Mark.
If the defections are allowed to go through, they will cut the PDP's majority in the 109-seat Senate by 26 seats, with the PDP down from 73 to 62 and the APC up from 33 to 44.
Analysts say Jonathan's dwindling support is tied to elections scheduled for February next year.
The president has come under mounting pressure from within his own party not to run and instead throw his support behind a Muslim candidate from the north.
Jonathan, who stepped up from vice-president to be acting head of state when former president Umaru Yar'Adua fell ill and later died in 2010, is a southern Christian.
He is also alleged to have promised to serve only one, four-year term after winning a popular mandate at the last elections in 2011.
All but two of the 11 senators seeking to defect are northern Muslims.
The upper house is a powerful institution in Nigeria, as all bills require approval from senators before entering into law and senators can themselves propose legislation.