Barclays customers will not be able to manage their accounts online, by phone or by app between Saturday night and Sunday afternoon as the bank carries out work on its systems to meet new regulations.
From 11.30pm on Saturday until 3.30pm the next day, millions of people will be unable to check their balances, make new payments or transfer money via the Pingit app.
However, debit and credit card transactions and ATM withdrawals will be unaffected and payments arranged prior to the outage will be sent and received as normal.
The planned outage is to let Barclays restructure its organisation to meet new ring-fencing legislation designed to prevent the kind of bank bailouts needed by Lloyds and RBS nearly a decade ago.
Hundreds of IT staff will work over the Easter weekend, moving some 24 million accounts to the new ring-fenced bank, separate from riskier investment banking operations.