"There is a monumental crisis within our country," said Juan Carlos Giordano, a socialist lawmaker who joined the march.
"Argentina is a capitalist semi-colony in the chains of the IMF. Today we are here to say we need a second independence. Argentina must break its ties with the IMF which is the Spanish Empire of the 21st century."
Fernandez's government was thrown into turmoil a week ago with the abrupt resignation of moderate Economy Minister Martin Guzman, a close ally to the president who had spearheaded talks with the IMF. He was replaced by economist Silvina Batakis.
Batakis, seen as closer to the left-wing of the ruling coalition than Guzman, spoke with the IMF on Friday and has pledged economic stability despite concerns over a populist policy shift that have dragged down bonds and rattled the peso.