Two large unions in Brazil are refusing an invitation to meet with acting President Michel Temer, underscoring the challenges facing the new leader of Latin America's largest nation amid a divisive impeachment process.

Temer assumed the presidency last week after President Dilma Rousseff was impeached and suspended for allegedly employing accounting tricks to hide gaping deficits in the federal budget.

Temer called for the unions to meet Monday to discuss reforms to the country's pension system, something that analysts say is necessary to begin pulling Brazil from its worst recession since the 1930s.

Several unions say they'll attend Monday's meeting, but two major groups are holding out. One of them is the Central Workers union. It says it "won't recognize putschists as governors" and it calls for Rousseff's return.