The workers assembled at Sher-e-Kashmir Park and started marching towards Lal Chowk area of the city raising slogans in favour of their demands, a police official said.
He said as soon as the protesters crossed the Polo View crossing, police intercepted them and asked the protesters to disperse peacefully.
However, they refused to pay any heed and tried to march ahead.
The police used batons to disperse the protesters and took over 30 of them into preventive custody, the official said.