In a hard-hitting speech, to be given on Saturday, Senator Dastyari will call 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 federal leader Bill Shorten, who hails from the Victorian Right, Senator Dastyari will concede in the speech that while offshore processing has proved 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.

This includes the secrecy of Operation Sovereign Borders, but there has been no suggestion it is preparing to rethink its policies.

But Senator Dastyari will say the ALP needs to adopt policies that are ''both firm and fair''.

''I think that future generations will look back on this period in our history with the same sense of embarrassment that we look back on the White Australia policy,'' he will say.

''Labor is and continues to need to be prepared to have an open debate about the future of our migration policies. The fact is, over the past few years, we tossed and turned on these issues.''

The speech, to mark the Iranian new year festival of Nowruz, will be the first time the Iranian-born senator has spoken publicly about the death of Iranian asylum seeker Reza Berati on Manus Island last month.

The senator will say he was shocked by the ''brutal murder'' and that he will not allow the Australian government to criminalise and further ''persecute young families fleeing their homes''.

''It could easily have been me and my sister,'' he will say.