On August 18, the Szczecin Shipyard joined the strike, under the leadership of Marian Jurczyk. A tidal wave of strikes swept the coast, closing ports and bringing the economy to a halt. With "KOR" assistance and support from many intellectuals, workers occupying factories, mines and shipyards across Poland joined forces. Within days, over 200 factories and enterprises had joined the strike committee. By August 21, most of Poland was affected by the strikes, from coastal shipyards to the mines of the Upper Silesian Industrial Area (in Upper Silesia, the city of Jastrzębie-Zdrój became center of the strikes, with a separate committee organized there, see Jastrzębie-Zdrój 1980 strikes). More and more new unions were formed, and joined the federation. In September 1980 in Prudnik, over 1500 workers of ZPB "Frotex" along with other factories and firefighters from Prudnik's fire brigade went on the biggest anti-communist strike in Opole Voivodeship.