Lawmakers wore the green uniform of the Guards in a display of solidarity at the legislative session, where they chanted “Death to America”, “Death to Israel” and “Shame on you, Europe”, state television footage showed.
Slamming the bloc’s “irresponsible action”, speaker Mohammad Bagher Ghalibaf said that under “Article 7 of the Law on Countermeasures Against the Declaration of the IRGC as a Terrorist Organisation, the armies of European countries are considered terrorist groups”.
It remained unclear what immediate impact the decision would have.
The law was first passed in 2019, when the United States classified the Guards as a terrorist organisation.
Sunday’s session was held on the 47th anniversary of the return from exile of the late Ayatollah Ruhollah Khomeini, who founded the Islamic republic in 1979.
The Guards are the ideological arm of Iran’s military, tasked with safeguarding the Islamic revolution from external and internal threats.
They have been accused by Western governments of orchestrating a crackdown on a recent protest movement that left thousands dead.
Tehran has attributed the violence to “terrorist acts” fomented by the United States and Israel.
The European Union agreed on Thursday to list the body as a “terrorist organisation” over the response to the protests.
The step matched similar classifications enacted by the United States, Canada and Australia.
Ghalibaf said the decision, “which was carried out in compliance with the orders of the American president and the leaders of the Zionist regime, accelerated Europe’s path to becoming irrelevant in the future world order”.
The move, he added, had only increased domestic support for the Guards.
The legislative session came as Iran and the United States have traded warnings and threats of potential military action.
Tehran’s response to the protests prompted US President Donald Trump to threaten to intervene, dispatching an aircraft carrier group to the region.
In recent days, however, both sides have insisted they remain willing to talk.