Hundreds of thousands of Colombians have joined street demonstrations against the policies of President Juan Manuel Santos.
Students and lecturers protesting against proposed university reforms were joined by trade unionists demanding improved conditions.
Colombia's main trade union federation, the CUT, said 1.5m people joined the demonstrations in cities nationwide.
The protests are the biggest since President Santos took office in August.
There were some disturbances in the capital Bogota and in the city of Pereira, where police used tear gas to disperse crowds.
But otherwise the protests are reported to have been peaceful and good-natured.
Colombia's intelligence agency, DAS, had warned that the Farc and ELN left-wing guerrilla groups might seek to provoke violence during the demonstrations.
Defence Minister Rodrigo Rivera said the security forces would respond with "severity" to any disorder.
Students groups are opposed to government plans to bring private funding into the public university system.
Trade unions are demanding measures to reduce unemployment, as well as more action to protect union activists from attack.