SEOUL, April 16 : Samsung Electronics asked a court on Thursday to block its South Korean labour unions engaging in illegal activities during strike, a spokesperson said, as a wage dispute threatens to disrupt operations at the world's top memory chipmaker. Unionised workers at Samsung last month voted to authorise strike plans and threatened to walk out for 18 days from May 21, should they fail to agree on a wage deal with management. The unions also plan to hold a major rally on April 23,