Former German Chancellor Angela Merkel has issued rare public criticism of her successor as the country’s center-right leader, the front-runner in Germany’s election next month, for putting to parliament proposals for tough new migration rules that only passed with the help of a far-right party.

BERLIN — Germany’s parliament is expected to vote Friday on an opposition bill calling for tougher rules on migration that could become the first legislation to pass thanks to a far-right party — adding to a controversy about the attitude of the front-runner in Germany’s upcoming election toward the far right.