Brazilian police and striking subway workers clashed Monday in a central commuter station, with union officials threatening to maintain the work stoppage through the World Cup opening match here this week.

Authorities are deeply worried about the strike because the subway is the main means of transportation for World Cup fans who will attend Thursday's opening match when Brazil takes on Croatia. The stadium is about 20 kilometers (12 miles) east of central Sao Paulo, where most tourists stay.

There were hopes the work stoppage may come to an end _ early Monday afternoon union officials were sitting down for the first time in days with government authorities in an attempt to end the strike. Last year, a fare increase was reversed after violent protests broke out.

Earlier Monday, riot police firing tear gas forced about 100 striking workers out of the station as the strike threw Sao Paulo's normally congested traffic into chaos for a fifth day. About half of the city's subway stations were operating, but with greatly diminished service.