Prime Minister Scott Morrison has slammed wharfies' industrial action in pursuit of 6 per cent a year pay rises as "straight-out extortion" as supply chain delays at ports around the country threaten to hold up Christmas stock.

Patrick stevedores warned on Tuesday that more than 100,000 containers faced delays if the wharfies' partial work bans continue into next week, with 38 ships held up around Australia and en route from Asia and operations unlikely to return to normal for up to three months.