Update: On Wednesday, Visa followed its statement from earlier this week regarding sanctions being imposed on Russian banks, with a disclosure noting that about 5% of its revenue in fiscal year 2021 derived from Russia and Ukraine. In the disclosure, as part of a filing with the Securities and Exchange Commission, Visa said its revenue from Russia was about 4%, including domestic and cross-border activities, and was about 1% from Ukraine.

A Visa spokesperson declined to name the banks. "Visa is in the process of complying with all applicable global sanctions," the company said in the filing. "As part of that compliance, we have suspended access to Visa for certain clients. It is difficult to reasonably estimate the full potential financial impact of this situation on Visa at this time."

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The No. 2 U.S. card company Mastercard disclosed that its business may be more vulnerable to a potential financial impact from sanctions in Russia than some analysts previously expected.

The Purchase, New York-based company said late Tuesday in a filing with the Securities and Exchange Commission that about 4% of its annual revenue derives from business related to Russia and about 2% derives from Ukraine. 

The disclosure comes a day after the U.S. card giants, including Mastercard’s larger rival Visa, said in statements that they would comply with government sanctions that called on them to block Russian banks from using their networks. The government sanctions were imposed in response to Russia’s invasion last week of Ukraine.

"While our global business fundamentals remain strong, Russia and Ukraine are important contributors to our overall company net revenues," Mastercard said in the filing.

Analysts last week estimated that the two big U.S. card companies received about 2% of their annual revenue from the Russian region, based on the companies’ revenue disclosures from that area in 2014 (companies don’t necessarily regularly disclose income by region). 

But that pointer from nearly a decade ago was apparently off. Baird Equity Research acknowledged the revelation in a research note, blaming a false lead from Russia’s relatively small population. "Russia (1.8% of global population) and Ukraine (just over 0.5%) are surprisingly bigger portions of (Mastercard) revenue than we expected, as we would’ve thought the percentage of revenue would more closely match the percentage of global population," the Baird note Tuesday said.

The Baird note went on to predict the impact to Visa would be similar, or perhaps slightly lower because Visa has less overall international exposure as a percentage of its revenue. 

American Express chimed in late Tuesday with a statement as well, noting that its business in Russia is "small," with just one partner that issues cards and a "handful" that service merchants.

"Since the beginning of this crisis, we have been complying with U.S. and international sanctions, which has resulted in us halting relationships with impacted bank partners in Russia, and we will continue to comply with all relevant laws as the situation evolves," American Express said in the statement.

That company also noted that it has prepared its cybersecurity for any fallout from the conflict. "American Express is taking all necessary steps to detect, prevent, and respond to any malicious activity through our layered defenses," the company said. "We remain vigilant and will continue to monitor this situation for any threats posed to American Express."

American Express also pledged $1 million to international relief organizations seeking to provide aid in the region, following the lead of Mastercard and Visa, which said earlier in the week that they would donate $2 million for humanitarian relief in the area.