Frontier Airlines and Rainbow Rewards Colorado, Inc. have announced a partnership that will bring added muscle to holders of Frontier Airline’s EarlyReturns MasterCards.

Denver-based Rainbow Rewards is a free credit and debit card rewards program for consumers that allows members to earn cash-back rewards by shopping with certain local and national merchants. In addition, every transaction provides a contribution to dozens of local charities through local chapters of United Way.

As a result of Frontier’s participation, all Rainbow Rewards members, including Frontier MasterCard holders, can choose to exchange their earned cash for Frontier EarlyReturns miles.

With the addition of Frontier Airlines cardholders, Rainbow Rewards will have over 200,000 credit and debit cards in the program. The program currently has over 1,000 local businesses and online national retailers.

Membership in Rainbow Rewards is free to Frontier MasterCard holders. Frontier MasterCard holders who provided their email addresses to Frontier’s card issuer and have elected to receive offers from partners are automatically enrolled in the Rainbow Rewards program if they choose not to opt-out during the opt-out period. Frontier cardholders who have not provided their email addresses who wish to participate can still enroll in Rainbow Rewards at no cost by going to http://www.rainbowrewards.com and registering. Cardholders who were automatically enrolled but wish to opt out of the program can also do so online.