Visa Canada says its network is back up and running after a countrywide outage for customers Monday.

Many customers across the country were unable to use their credit cards during the outage, which Visa blamed on a "third-party" service provider.

CIBC, Royal Bank of Canada and TD Canada Trust all said their customers were among those affected by the outage.

Hundreds of credit card users across the country took to Twitter to complain that their cards were being declined when they tried to use them, sending "Visa" to the top of the Twitter trending chart.