The government will face a challenge from unions tomorrow over the impact of migration on Labour's core working-class voters… The Guardian has obtained submissions made to government by the leading unions which catalogue the replacement of traditional jobs with cheaper, casualised and often migrant labour in most industrial sectors... Their evidence…alleges exploitation of migrants and racial tension as a two-tier workforce has emerged… Unions will demand tomorrow that agency staff are given the same employment rights as permanent staff, to protect both local and migrant workers. [article cites case studies of A&P, Dawn Group, BMW, St Ives, Trinity Mirror, Quebecor World, Corus, Harper Collins, Coca Cola, Chep UK, Grampian, Moy Park – includes company responses]