Polling cards and campaign material may arrive together
Polling cards may be delivered alongside referendum material due to contracts An Post has with several organisations for 'leaflet drops'.
The company has been delivering campaign material for organisations on both sides of the debate, as well as information from the Referendum Commission in recent weeks, ahead of Friday's vote.
Those contracts continue even when An Post begins to deliver polling cards to voters.
It is "quite possible" a person's polling card may arrive at the same time as material advocating a Yes or No vote, a spokesman for An Post confirmed. However, staff are under "strict instruction" to ensure the material is kept physically separate. This means no polling card should be folded in or appear to accompany any campaign material.
The potential for both to arrive at the same time is due to logistics. This has been the case in previous referendums, as well as elections.
Polling cards are being delivered to thousands of households around the country.
More than 3.2m people are registered to cast their vote. The number of newly registered voters is expected to surpass the number that registered in advance of the marriage equality referendum.