In 2006, Americans donated nearly $300 billion to charities and other nonprofit organizations by using affinity credit cards, which make a small donation to a charitable group with every purchase.

But according to the editors of Consumer Reports’ Money Adviser, users could feel a decidedly uncharitable pinch in the form of high finance charges, depending on the card and their payment habits.

How affinity cards work

Affinity cards are bank credit cards that are generally tied to charitable organizations, educational institutions and nonprofit groups. Typically, the cards are emblazoned with the charity’s logo and often a heartwarming image that is a “mini billboard” for a cause – a baby seal, Morris the Cat or a heron.

Each time a shopper uses an affinity credit card, the issuing bank pays a small percentage of the purchase, cash advance or balance transfer to the organization it’s tied to. In rare cases, the donation amount is a full 1 percent, as with the World Wildlife Fund and the World Missions Visa cards. The amount is usually much less, about 0.25 to 0.50 percent, or 25 to 50 cents for every $100 charged.

Unlike other forms of charitable giving, cardholders can’t claim a year-end tax deduction for gifts made through their cards. Nor can they ensure that the amount earmarked for the charity goes to the program they support rather than to overhead or administrative fees, although some charities specifically state that the donation goes directly to projects.

Watch rates, terms

Affinity cards aren’t necessarily charitable to the cardholder. Like any credit card, they can charge high interest rates and other fees, or carry unfavorable terms. Affinity cards that also pay rewards tend to have higher rates, so they might not be a good choice for people who don’t pay off their balance in full each month.

It pays for cardholders to think about them rationally – for example, to consider the option of getting a tax deduction for their contributions. It’s also important to note that the percentage that goes to charitable organizations has changed little since the cards were introduced in the 1980s.

And while supporting a pet cause may give cardholders a warm, fuzzy feeling, they should also examine the bank that’s issuing the card and stands to profit from its use. A credit card may have a picture of a whale on it, but the cardholder may not support the actions of the bank.

Affinity cards are no longer the only game in town for charity-minded spenders. Many general-purpose and rewards credit cards now offer their holders the option of donating earned points or cash rewards to a number of charities. Examples include the relaunched BankAmericard and American Express cards.

The charitable and less so

Here’s a sample of affinity cards, with their interest rates plus the donation amount or percentage. None has an annual fee.

¢ ASPCA Platinum Visa (www.aspca.org) – 13.49 percent to 22.49 percent; $75 to ASPCA on first purchase, then 0.2 percent of purchases.

¢ Make-a-Wish Platinum Visa (www.wish.org) – 15.24 percent (prime rate plus 7.99 percent); 0.65 percent of purchases.

¢ Sierra Club Platinum Plus MasterCard (www.sierraclub.org) – 9.99 percent to 15.99 percent; donation terms not disclosed.

¢ Working Assets Visa Signature (www.workingassetscard.com) – 9.99 percent to 15.99 percent; 10 cents for every transaction, tree planted for every tank of gas charged.

¢ World Wildlife Fund Platinum (www.worldwildlife.org) – 0 percent for up to 12 months, then 11.49 percent to 22.49 percent; 1 percent of purchases plus $50 for signing up online.