Processing asylum seekers who are already in Australia won't result in a resurgence of people smuggling boat arrivals, the federal opposition says.

The High Court has ruled the federal government can't limit how many refugee protection visas it can issue, dealing a blow to its refugee policy.

But Opposition immigration spokesman Richard Marles said the High Court's ruling only applies to asylum seekers who arrived before July 19, 2013.

It was on this date former prime minister Kevin Rudd announced arrangements to send asylum seekers to Papua New Guinea.

"This decision has no bearing on whether or not we will see asylum seeker vessels coming to Australia," Mr Marles told reporters on Saturday.

"Whatever you do in relation to the people who are already here can be neither a deterrence or incentive."

Immigration Minister Scott Morrison signed a legal instrument in March saying a maximum of 2773 protection visas could be granted in the year to June 30.

That maximum having been reached, no new protection visas could be granted.

A High Court challenge by two asylum seekers led to judges unanimously supporting the pair's entitlements to refugee protection.

The judges said the section of the Migration Act under which the minister had made his original ruling was invalid.

Mr Marles also said Labor deserved the credit for stopping the boats, as it was Labor's PNG solution that had proved the greatest deterrent to people smugglers.

He said Mr Morrison had attacked Labor for offering cash incentives to asylum seekers to return home, only for the Coalition to triple those payments when in government.

AAP