An Associated Press investigation has found that two of America's biggest retail banks — Chase and Wells Fargo — are quietly using some callers' voiceprints to fight fraud.

Privacy advocates and legal experts question the practice. Customers who call bank support numbers are often informed that their calls may be monitored or recorded, but aren't asked to give their consent for biometric analysis.

Fraud blacklists are among the growing everyday uses of speaker recognition, once a high-tech tool used by security agencies. Many governments and businesses use voiceprinting.

A recent Associated Press survey of the market found that more than 65 million people worldwide have had their voiceprints taken.