The document threatened that the ZANU PF, which has kept Mugabe in power for decades, would launch impeachment proceedings under Section 97 of the country's constitution [text, PDF] if he did not step down by noon on Sunday.
Mugabe has been at the forefront of Zimbabwe's government ever since the country was founded in 1980. Calls for his resignation were prevalent a decade ago when economic mismanagement devastated the country's economy, resulting in currency hyperinflation which has been estimated [CATO study, PDF] to have reached a monthly inflationary rate over 79 billion percent at its worse in 2008.
In the country's 2008 presidential election [JURIST news archive], Mugabe came in second during a highly contested and violent first round of voting and managed to convince his opponent to drop out before the second round took place.
Recently Mugabe ousted his longtime ally and vice president Emmerson Mnangagwa [BBC profile] in an apparent attempt to consolidate power for his wife, Grace Mugabe [BBC profile]. This triggered a backlash from the military and the ZANU PF, both of which have been instrumental in the maintenance of his authority for all these years as a "soft coup" was launched against Mugabe last week.