Four months of student-led demonstrations have drawn in teachers, farmers and others to become the biggest threat yet to President Aleksandar Vucic's decade-long rule, with many Serbians denouncing corruption and incompetence in government.
At the legislative session, after the ruling coalition led by the Serbian Progressive Party (SNS) approved the agenda, some opposition politicians ran out of their seats towards the parliamentary speaker and scuffled with security guards.
Others tossed smoke grenades and tear gas, with live TV showing black and pink smoke inside the parliament, which has also been the scene of brawls and throwing of water in the decades since the introduction of multi-party democracy in 1990.
Speaker Ana Brnabic said two MPs were injured, with one, Jasmina Obradovic of the SNS party, suffering a stroke and in critical condition.
"The parliament will continue to work and to defend Serbia," she told the session.
As the session continued, ruling coalition politicians debated while opposition MPs whistled and blew horns.
Opposition deputies also held signs reading "general strike" and "justice for the killed" while outside the building protesters stood in silence to honour 15 people killed by a railway station roof collapse that was the spark for the protest movement.
Protest leaders called for a major rally in the capital Belgrade on March 15.
The ruling coalition says foreign intelligence agencies are trying to destabilise Serbia and topple the government by backing the protests.
Parliament was due on Tuesday to adopt a law increasing funds for universities - one of the main demands of students blocking faculties since December.
Parliament had also been due to note the resignation of Prime Minister Milos Vucevic.
But other items put on the agenda by the ruling coalition angered the opposition.
