Riot police broke up a sit-in by thousands of striking bank workers Wednesday. But union leaders vowed to ignore government threats and push ahead with the work stoppage, which has shut down Kookmin Bank and Housing and Commercial Bank.

Columns of police armed with clubs and shields marched into the crowd of strikers in a bank training center in Ilsan where they had been holding their protest for six days. But no injuries were reported.

Before the raid, police helicopters clattered overhead, the wind from their rotors tearing off the canvas walls of the workers' tents.

The operation came amid government fears that other workers would stage sympathy strikes, expanding the protest.

Fearing massive layoffs, the unions launched the strikes Friday to protest plans to merge the two major commercial banks.

The walkout has virtually shut down the two banks. The two banks handle a quarter of the country's retail banking.

Some 15,000 union workers have slept in tents in an arena or on thin Styrofoam boards in the Kookmin training institute, defying subzero temperatures as well as police orders to go home.