Congressional leaders made the announcement on Saturday after receiving the report from a four-member panel that recommended the mayor stand trial for allegedly ignoring a court order halting the construction of an access road to a capital hospital.

López Obrador will be called to the Chamber to argue his defense before the vote. If the federal lawmakers vote that there is sufficient evidence for him to stand trial, the mayor will likely be disqualified from running in the 2006 presidential elections, regardless of whether he is found guilty or innocent.

Of the field of potential presidential candidates, López Obrador has consistently led the polls.

In his daily press conference, the mayor seemed unconcerned by the impending vote and called on his followers to protest peacefully. He said the city will continue to run smoothly regardless of the result of the congressional vote.

"We are going to continue the work that we have started," López Obrador said, referring to public works projects his government has initiated in the capital. "We have to keep working and guarantee services, social programs and public security."

Demonstrations to support the massively popular mayor are scheduled to begin on Monday. However, local authorities have asked the mayor's followers not to physically attack its opponents, occupy government offices, block roads and highways or confront federal security around the Congress.

Protests are expected outside of Mexico City as well, and various farmer and campesino groups on Saturday said they would be supporting López Obrador, who belongs to the left-leaning Party of the Democratic Revolution (PRD).

The PRD is only the thirdlargest party in Congress, while the Institutional Revolutionary Party (PRI) holds a plurality and President Vicente Fox's National Action Party (PAN) has the second-largest representation. If the vote follows party lines, the desafuero will proceed.

However, some PRI and PAN members have expressed doubts about the process against López Obrador, which would effectively remove the nation's most popular candidate from the 2006 election. The outcome of the process is uncertain if lawmakers are allowed to vote independently.

PRI leaders have assured journalists this week that the party has enough votes in the Congress for the charges against the mayor to proceed.

According to polls by the Mitofsky Group, the proportion of Mexicans favoring him for president has risen from 27 percent last May, when proposals to impeach him were first made, to 37 percent now.