JPMorgan has left more than a third of its US bank branches open for business in the runup to Christmas to help customers affected by last week's data breach at discount retailer Target.
Many branches were open in the eastern US and in California, with a priority on those in close proximity to major shopping centres.
Earlier, JPM informed two million customers, who used Chase brand debit cards at Target stores in the US, that they would have to cope with lower cash withdrawal and spending limits.
The precautionary move, aimed at protecting accounts, would apply to customers who used their bank debit cards at Target stores from 27 November to 15 December.
On 22 December, JPM told those customers that they could use their debit cards to withdraw just $100 a day from teller machines and make purchases worth $300 a day. The normal daily debit card limits are $200 to $500 for cash withdrawals and $500 for purchases.
Customers who required more cash could access their accounts at open branches. The new limits would affect about 10% of Chase debit cards, according to a bank spokeswoman.
The banking giant also said it would issue fresh debit cards over the coming weeks.
JPM said in its notice to customers that it realised its action "could not have happened at a more inconvenient time with the holiday season upon us."
Meanwhile, representatives for other banks, including Bank of America and Citigroup told Reuters they had taken steps to protect customer accounts but did not divulge details.
Target said last week that data from about 40 million credit and debit card accounts could have been stolen during the Thanksgiving weekend, confirming media reports that said the US Secret Service was investigating a suspected data breach at America's second-largest discount retailer.
Target said on 19 December that "it is aware" of the data theft and that it has "identified and resolved the issue".
Purchases made at Target's US stores between 27 November and 15 December "may have been impacted", according to a Target statement.
Target has 1,797 stores in the US and 124 in Canada. The company's stock finished 0.55% higher in New York on 20 December and has gained 5.61% so far this year.