The drivers' union AKT has shut down bus services in Jyväskylä, Kuopio, Lahti, Oulu and Pori because employers did not agree to talks on the issue of part-time workers. Employers have insisted the strike is illegal and rebuffed calls for negotiations.

Around 1,300 drivers from the Connex and Concordia companies are already protesting over job security and working hours in Espoo and Vantaa. The strike expanded to include about 2,000 drivers.

Drivers suspect that the bus companies plan to introduce more part-time contracts.

Meanwhile the stakes are rising -- and the rhetoric getting tougher on both sides.

The Confederation of Finnish Industries, or EK, warns that the strike could threaten ongoing central incomes agreement negotiations. The union scoffs at that suggestion, while alleging that foreign drivers are being intimidated with threats of deportation or losing their homes.

A Labour Court on Wednesday declared the strike illegal and imposed a fine of 20,000 euros on the union. On Friday it raised that to 29,000 euros.

The strike has paralysed virtually all internal bus routes in Espoo and Vantaa and half of regional bus routes to and from Helsinki. However, some services have been operated with the help of supervisory staff.

In September, drivers of Helsinki City Transport, HKL, went on strike for one day to protest merger plans.