Foreign nationals would be excluded from most benefits under a Reform UK government, the party has said.
The ban, part of a proposed overhaul of Britain's benefits system, would include European Union (EU) nationals with settled status in the UK.
It would require renegotiating the UK's Brexit deal with the EU, potentially meaning that British expatriates living in the EU could lose equivalent rights.
Reform claims the policy would save £21bn a year by its fifth year, but Labour insists the "vast majority" of migrants have no access to benefits and the Conservatives have dismissed the plans as "cobbled together".
It is the latest announcement ahead of a speech on Monday by Reform's shadow chancellor Robert Jenrick to formally unveil the party's welfare plans.