In the largely Kurdish southeast, authorities slapped a ban on celebrations of May Day in the cities of Diyarbakir and Siirt. Local trade unionists there said they would hold a one-day hunger strike to protest the ban.
In the eastern city of Tunceli, authorities detained 20 people, including local officials of the pro-Kurdish People's Democracy Party, for attempting to make an unauthorized public press statement to mark May Day, the Anatolia news agency said.
Political parties, trade unions and student groups made up the majority of a large march through central Istanbul. Many marchers waved Palestinian flags, while others carried placards condemning the government's IMF-backed economic policies, which will see tens of thousands of public sector workers laid off this year.
"A thousand greetings to the Palestinian resistance," were among the slogans.
Some 10,000 police were deployed along the route of the march. There were no initial signs of trouble at a celebration which has seen clashes between police and leftist groups in previous years.
Rallies were also held in several other Turkish cities, including the capital Ankara.