A potentially costly blunder for Westpac.

The Commerce Commission has filed High Court proceedings against Westpac, alleging the bank breached the Consumer Finance Act by failing to provide key information required under the law.

READ MORE: Watchdog takes legal action against Westpac NZ over credit card blunder

Westpac self-reported the issue, admitting it failed to provide disclosure information to personal credit card customers.

Andrew Kelleher of JMI Wealth told Mike Yardley 19,000 personal credit card customers were impacted.

He says the Act allows for damages of between $200 and $6000 per customer.

Westpac is blaming an error during an IT upgrade for its blunder.