WARSAW—Poland’s government is drafting new laws to rush its purge of the Supreme Court, racing ahead of efforts by the European Union to halt what authorities in Brussels view as a rapid erosion in rule of law.

The moves dampen hopes held by some EU leaders and officials that legal proceedings against Poland could slow Warsaw’s drive to dismiss as much as a third of its Supreme Court bench. Instead, Poland’s nationalist government appears set to accelerate its clash with Brussels, which worries the country is removing one...