The refusal follows "threats of the future government of completely destroying the democratic order and the rule of law."
Brazil's Workers Party (PT) released a statement on Friday confirming it will not take part in the swearing-in ceremony of far-right President-Elect Jair Bolsonaro on January 1.
The party boycott follows several irregularities during the elections. The current situation in Brazil "makes it mandatory to denounce and protest against the threats of the future government of completely destroying the democratic order and the rule of law in Brazil," the PT said.
The Workers Party has recognized the results of the elections, but it "does not represent an endorsement of an authoritarian, antipopular and unpatriotic government, marked by open racist and misogynist positions, reportedly linked to a program of civilizational setbacks.
"The PT caucuses will not be present at the inauguration ceremony of the new president in the National Congress... but that does not prevent us from denouncing the irregularities of the 2018 electoral process that was characterized by the impeachment coup, by the illegal prohibition of Lula's candidacy and the criminal manipulation of social media against our candidate Haddad."
The PT is concerned because "the hatred of the president-elect against the PT, popular movements and former president Lula is the expression of a project that, assaulting the institutions, intends to impose a police state and tear apart the historic achievements of the Brazilian people."
"We were built on resistance to the military dictatorship, so we reaffirm our commitment to fight for social rights, national sovereignty and democratic freedoms," the statement concluded.