Labor has called for the Turnbull government to admit defeat on its controversial tightening of Australian citizenship laws, demanding the immigration department process applicants under the existing protocols.

Immigration Minister Peter Dutton in April announced an overhaul of the citizenship process, including a tough English language test and the requirement for applicants to spend four years as permanent residents.

But the bill is poised for defeat in the Senate, where it is staunchly opposed by Labor, the Greens and the Nick Xenophon Team, who together hold enough votes to block the legislation.

Despite the measures not yet being law, prospective Australian citizens are informed the changes will be backdated to April 20, when the policy was announced. All applications since April 20 are being processed under the new rules.