Workers in South Africa's petroleum, pharmaceutical, chemicals and paper sectors will go on strike on July 11 over wages, a union official said on Thursday.

The Chemical, Energy, Paper, Printing, Wood and Allied Workers Union which represents 70,000 employees, is seeking a 13% wage increase, almost triple the inflation rate, for 2011/12 and a minimum wage of 6,000 rand (about €630) a month.

 Employers are offering a 4 to 7% increase, the union said last week. Companies that will be impacted include Aspen Pharmacare, Africa's biggest generic drug maker.