Christian leaders are urging the federal government to raise the humanitarian intake of Afghan refugees from 3,000 to 20,000.

The Christians United for Afghanistan campaign is also calling for a special one-off refugee intake - outside of the existing humanitarian program - similar to that announced by the Abbott government in 2015 when 12,000 places were allocated for Syrian refugees.

Catholic Bishop of Parramatta, Vincent Long, says Australia has had a "long tradition of generously resettling refugees and displaced persons who flee their home countries due to war, conflict and violence."