Ruling coalition leaders Asif Ali Zardari -- the widower of slain former premier Benazir Bhutto -- and Nawaz Sharif announced on Thursday that they would seek Musharraf's impeachment for allegedly mismanaging the country. "The national assembly session has been summoned at 5:00 pm (1100 GMT) for Monday," an assembly official told AFP. Pakistan People's Party spokesman Farhatullah Babar said the session would set into motion the process to impeach Musharraf. "The session has been summoned in connection with impeachment of the president," Babar said. He added "a notice for impeachment will be served on President Musharraf during the session, starting Monday". Under the constitution, at least half of either the national assembly, the lower house of parliament, or the Senate, the upper house, must sign a written notice of the intention to impeach the president. The speaker of either chamber then has three days to give it to the president. Then the speaker must summon a joint sitting of the houses "not earlier than seven days and not later than 14 days" after the president receives the notice. The sitting would then "investigate or cause to be investigated" the charge sheet. Impeachment requires a two-thirds majority in the upper and lower houses of parliament under Pakistan's constitution. It would be the first time in Pakistan's 61-year history that a president has been impeached. The coalition is currently several seats short of the 295 votes it requires out of the 439 in the Senate and National Assembly to remove Musharraf. Zardari's Pakistan People's Party and Sharif's Pakistan Muslim League-Nawaz, together with smaller coalition partners, have 266 seats and need a further 29 MPs, mainly from the troubled tribal belt bordering Afghanistan. But the key factor in Musharraf's decision is likely to be the support he gets from the army. Musharraf, a key US ally in the "war on terror" quit as army chief last November. The United States, which counts Musharraf as a linchpin in the fight against Al-Qaeda and the Taliban, said that the impeachment was an "internal" matter.