Holders of MARTA Breeze cards will be unable to check their card balances online or by phone during a system upgrade for nearly four days beginning Friday night, the transit agency announced.

The upgrade is scheduled to begin at 9 p.m. Friday and end at 6 a.m. Tuesday.

During the upgrade, customers still will be able to load Breeze cards and check balances at Breeze vending machines in transit stations and at RideStores, MARTA said.

For additional information, call the Breeze Customer Call Center at 404-848-5000 or visit its website.