BERLIN—German lawmakers adopted the country's first national minimum wage on Thursday despite complaints by trade unions that the program was ridden with loopholes and warnings from business that it could be a job-killer.

Wrapping up months of tough negotiations, parliament's lower house adopted a statutory wage floor of €8.50 ($11.61) an hour. The minimum wage will be compulsory from 2015 with a two year-transition period granted to some sectors.

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