NSW Labor powerbroker Sam Dastyari has lashed his own party's asylum seeker policies and predicted Australians will one day be as embarrassed by offshore processing as they now are by the White Australia Policy.

In a hard-hitting speech that creates a political headache for Labor leader Bill Shorten, Senator Dastyari calls for renewed debate in the ALP over the offshore processing measures adopted by former leader Kevin Rudd.

In a clear sign of the gulf between the NSW Right factional powerbroker and the federal leader, who hails from the Victorian Right, Senator Dastyari concedes that while offshore processing has proven to be effective, "it is not something I am entirely comfortable with".

Labor has been critical of the government's handling of offshore processing on Nauru and Papua New Guinea since the election, including the secrecy of Operation Sovereign Borders but there has been no suggestion it is preparing to rethink its policies.

But Senator Dastyari said the ALP needed to adopt policies that were "both firm and fair".