The law would allow parliament to appoint 15 of 25 members of Poland's National Council of the Judiciary, a body of judges that nominates other judges. It would also allow for all current members to be dismissed.
The populist government in Warsaw says that the changes would help Poland's courts, known for working too slowly, to be faster and more efficient.
But human rights officials see the planned changes as part of a drive by the ruling Law and Justice party to cement power by weakening the constitutional system of checks and balances on the government.
Council of Europe Commissioner for Human Rights Nils Muiznieks said in a letter to Poland's parliament speaker, Marek Kuchcinski, that he worries the new changes planned for the judicial system would violate the separation of powers and the independence of the judiciary.
"In order to preserve the principles of separation of powers and the independence of the judiciary, the selection of members of the judiciary should be a decision process wholly independent of the government, so as to stave off the risk of any undue political influence," Muiznieks wrote. The Council of Europe is distinct from the EU and aims to promote human rights and democratic values.