For small business cards covered under mc zero liability, what are the time frames for customers to report unauthorized transactions?

Mastercard does not define a timeframe on their Zero Liability website

The two criteria to qualify for Zero Liability protections are:

You have used reasonable care in protecting your card from loss or theft; and
You promptly reported loss or theft to your financial institution.

I encourage my clients to define "prompt" in their cardholder agreements. Although regulation E does not apply to small businesses, defining prompt as "two business days after learning of the loss or theft of the access device" (borrowed from 1005.6(b)(1)) seems like a prudent timeframe.

I have my Mastercard and Reg E Error Resolution webinar coming up on October 16 that will address questions such as this.

VISA and Reg E Error Resolution is on October 13th.

Thank you, Brian!