German carmaker Opel, a loss-making unit of US giant General Motors, said Thursday it will reduce working hours at two key plants as demand in the European car market slumps. \"In consultation with the works\' council and the IG Metall labour union, Adam Opel AG will introduce short-time work at its plants in Ruesselsheim and Kaiserslautern from September. It was agreed that 20 working days would be cut between then and the end of the year,\" Opel said in a statement. \"The European car market is dropping dramatically,\" the statement said. \"Falling capacity utilisation can no longer be compensated with measures such as flexitime,\" said Opel\'s personnel chief Holger Kimmes. \"Short-time work is now the right way to bridge this weakness in the market.\" The head of the general works council, Wolfgang Schaefer-Klug, said the measure would \"secure jobs\" and help limit financial hardship for the employees concerned. The measure would be introduced both in the production operations, as well as in administration. Ruesselsheim is Opel\'s main production site and also its headquarters and employs a workforce of 13,800, with 3,500 in production, 3,300 in administration and a further 7,000 in engineering. \"Around half of the employees will be affected,\" Opel said. The Kaiserslautern plant employs a workforce of 2,500.