Around 15,000 workers at German car giant Volkswagen walked off the job Monday in warning strikes aimed at turning up the pressure on management in deadlocked wage talks, the AFP news agency reported. At VW's factory in Braunschweig, northern Germany, close to 3,000 workers downed tools for four hours overnight, with demonstrations staged at different gates of the factory, the IG Metall labor union said. Similar walkouts were staged at VW's other sites in Kassel, central Germany, and the northern plants of Salzgitter, Emden and Wolfsburg. The so-called Friedenspflicht deadline, banning industrial action during wage negotiations, ended last Thursday and already on Friday 4,000 workers walked off the job temporarily. As management and unions met for a sixth round of wage talks on Monday, both sides showed signs of digging in their heels. Europe's biggest car maker is seeking a two-year wage freeze for the 103,000 staff on German assembly lines and a 30 percent reduction in labor costs by 2011. IG Metall, for its part, is demanding job guarantees for 10 years and a 4-percent increase in wages.