The German Parliament's upper house has voted to introduce a mandatory national minimum wage, a challenge by the country's opposition to Chancellor Angela Merkel's government ahead of elections in September.

Opposition parties gained a majority in the upper house, which represents Germany's 16 states, when the center-left Social Democrats and Greens ousted Merkel's conservative-led coalition from government in Lower Saxony state in January.

That gives them a chance to put pressure on Merkel and showcase plans for Germany, which holds national elections Sept. 22, by sending policy initiatives to the government-controlled lower house, which will likely reject them. The upper house voted Friday to introduce an across-the-board national minimum wage of (EURO)8.50 ($11.15) per hour.

Merkel's coalition is divided on whether to introduce some kind of minimum wage.