Paraguay's parliament has voted to have President Fernando Lugo impeached after deadly land clashes last week.
The opposition-controlled lower house overwhelmingly approved the move.
The Senate quickly followed suit and announced it would hold the trial on Friday, giving the left-wing president 24 hours to prepare his defence.
Mr Lugo has faced severe criticism over his handling of a forced land eviction in which seven police officers and at least nine farmers were killed.
He has said he will not resign but will "face the consequences" of the trial.
Speaking on national television, Mr Lugo said: "This president announces that he is not going to present his resignation and that he will fully respect the constitution and the law to face the impeachment trial and its full consequences."
The Senate, the body which will decide whether or not to remove the president from office, is controlled by the opposition. Reports suggest only five out of 45 senators support Mr Lugo.
Following emergency talks, the Union of South American Nations said it would send an urgent mission of foreign ministers to Paraguay to "ensure the right to defend democracy".
BBC regional analyst Leonardo Rocha says South American countries are worried that Mr Lugo, Paraguay's first left-wing president, is the victim of a political trial by right-wing groups which held power for 61 years before his election in 2008.
The clashes in eastern Canindeyu province last Friday which sparked the impeachment proceedings left seven police officers and at least nine farmers dead.
More than 300 police officers tried to evict 150 landless farmers from an estate owned by a wealthy businessman who is also a political opponent of Mr Lugo.
The eviction escalated into violence and the farmers opened fire on the police.
Nine farmers involved in the clashes were charged with murder.
The farmers have argued the land was illegally taken during the 1954-1989 military rule of Gen Alfredo Stroessner and distributed among his allies.
Land disputes are not unusual in Paraguay, where a small fraction of the population owns about 80% of the land.
According to the Paraguayan Truth Commission, 6.75 million hectares of land were sold or handed over under "irregular circumstances" during military rule.
When he was elected in 2008, Mr Lugo campaigned for the needs of the poor and had promised land for some 87,000 landless families.
On Wednesday, in an attempt to calm tensions over the incident, Mr Lugo said he would open an investigation into what happened.
The interior minister and the chief of police have already resigned over the clashes.
Mr Lugo, who heads a coalition government, was elected four years ago.
Paraguay's constitution states that when a president is impeached, the vice-president must take over for the remainder of the original term in office.
His term ends in August 2013 and the next presidential elections are due in April of that year.