Enjoy reading these :)
http://www.s-cool.co.uk/a-level/economics/labour-markets/revise-it/the-equilibrium-wage
http://www.economicshelp.org/labour-markets/labour-market-imperfections.html
http://reedseconomics.blogspot.com/2009/01/labour-market-imperfections-trade-union.html
http://www.s-cool.co.uk/a-level/economics/labour-markets/revise-it/trade-unions