A postage due stamp is a postage stamp used to collect postal charges from the recipient: when a postal item is sent with insufficient postage or with unpaid postal fees; and for postal items whose delivery must be paid specifically by the recipient. Postage due stamps were distinguished by the fact that they were not sold to the public, but were affixed by postal employees to correspondence on which the sender had paid less than the current rate; the amount due was then collected from the addressee upon delivery of the correspondence. In the USSR, postage due stamps were issued until 1925.
From May to October 1925, two series of postage due stamps of various denominations were issued and used until February 1, 1926. Thereafter, instead of postage due stamps, postage due handstamps with the inscription "To pay" or "Surcharge" were used.