Director of cruise at the Barbados Tourism Marketing Inc., Cheryl Franklyn, described Carnival's decision "to lend the Fascination to the rebuilding effort "as honourable".
Carnival said FEMA only reached out after the line had already announced its upcoming resumption of San Juan cruises, giving just a few days' notice to customers.
Starting Sunday, a Carnival Cruise Line ship will serve as the new home for relief workers in St. Croix.
San Juan cruises were just days away from resuming. Numerous crew of the 2,056-passenger Fascination will remain on board during the charter period, while others will be shifted to other vessels or offered early vacation, Carnival said.
The Caribbean has always been a mainstay destination of Carnival with its ships having been historically deployed there for over 45 years.
Guests on the line's scheduled cruises for the period of the charter will receive a full refund and a future cruise discount.
All those guests who were booked on the canceled sailings are being compensated by Carnival Cruise Line.
Refunds will automatically apply to the initial payment method within three weeks.
Fascination will return to San Juan to operate Southern Caribbean cruises on February 18, after the ship gets a scheduled upgrade with a new restaurant, bar and other features.
The report also points out that other Carnival ships have been used by FEMA in the past after Hurricane Katrina in New Orleans.
Carnival joins Bahamas Paradise Cruise Line in chartering a ship to FEMA for hurricane relief efforts in the U.S. Virgin Islands.