Guatemala's first lady, Sandra Torres de Colom, says she will be a candidate to succeed her husband Alvaro Colom in presidential elections in September.
Ms Torres announced her candidacy for the governing party despite a constitutional ban on relatives of the president standing to succeed him.
Her lawyers argue that the ban infringes the right of all Guatemalans to stand for election.
Ms Torres said she responding to "popular clamour" for her to stand.
She announced her candidacy at a rally in Mixco, a poor suburb of Guatemala City.
Ms Torres, who as first lady has been supervising poverty relief programmes, said her aim was to build a Guatemala with "social peace and hope".
Opposition groups say her candidacy is prohibited by Guatemala's constitution, which prohibits close relatives of a president from standing to replace him or her.
"It is an unconstitutional candidacy, but we will have to go through all the processes that the law requires," said former Gen Otto Perez Molina, candidate for the right wing opposition Patriot Party.
The decision on whether Ms Torres can stand for president in September will rest with Guatemala's constitutional court.
If elected, she would would be Guatemala's first woman president.