Marijuana

Though it’s increasingly rare for merchants to refuse payment by credit card, it’s not unheard of. American Express AXP, -1.16% , Visa and MasterCard MA, -1.22% , for instance, officially forbid the use of its plastic for medical marijuana—even in Colorado, which this year became the first state to allow marijuana use for recreational purposes. However, some dispensaries in Colorado are flouting those rules, according to a recent article in The Wall Street Journal. American Express points to federal law, which still prohibits the use of marijuana even for medical or recreational purposes. MasterCard is seeking guidance from the federal government, a spokesman says. “We’re facing a situation where there’s an inconsistency between federal and state laws.”

Here are 9 other things you can’t buy with plastic.

— By Quentin Fottrell and Catey Hill

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Pornography

American Express has a total ban on sales of online pornography, which a spokeswoman says is intended to help in the fight against child pornography. Plus, consumers can’t always be sure of the security of such sites. MasterCard and Visa say their cards can be used for any legal purchase. Of course, there are millions of online pornography sites charging for membership and videos on the web, which makes it difficult for credit-card companies to be sure of the legality of the content.

Bloomberg

WikiLeaks contributions

In 2010, Visa and MasterCard prevented U.S. cardholders from using their cards to donate to the whistleblower website WikiLeaks, but the site now accepts payments from MasterCard. The site never accepted American Express, although it gives Amex as an option. “The site incorrectly lists Amex as a payment option,” a spokeswoman says. “The transactions would not go through.” In 2010, WikiLeaks collaborated with major media organizations to release U.S. State Department cables in a redacted form and, in 2011, published files relating to prisoners detained in Guantanamo Bay. In 2013, WikiLeaks assisted Edward Snowden—the former National Security Agency contractor who disclosed top NSA secrets to the media—in leaving Hong Kong for Russia.

Bloomberg

Casino gambling

Gambling is another area where some contend credit card restrictions don’t always make sense. While cardholders can’t buy chips with plastic, for instance, they can use their cards to get a cash advance at a casino’s ATM—cash they might then use to buy chips. “It’s arbitrary,” says Curtis Arnold, founder of the credit card comparison website CardRatings.com. (Processing online gambling transactions is illegal in the U.S.) But he says that credit card companies don’t want to make it easier for their customers to rack up debt at the roulette table using their credit cards. MasterCard can be used in states where there is legalized gambling for their own residents—in New Jersey, for instance—known as intrastate online gambling, a MasterCard spokesman says.

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Lottery tickets

Lottery rules are determined on a state-by-state basis. This is why some states let you buy lottery tickets with credit cards while others only allow cash purchases of lottery tickets, says Anisha Skar, an analyst with NerdWallet.com. In general, the states say that don’t allow credit card purchase because they want to prohibit consumers from going into debt by purchasing lotto tickets, experts say. Skar notes that not all credit cards allow you to buy lottery tickets either: American Express, for example, prohibits this behavior.

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Anything under $10

Under the Dodd-Frank Consumer Protection and Wall Street Reform Act passed by Congress and signed into law in 2010, retailers are allowed to set a minimum amount of up to $10 on credit card purchases. Every time a customer uses a credit card in a store, the merchant must pay an interchange or “swipe” fee, and credit cards that are loaded with benefits for the consumer are often the most expensive for the merchant to process, Arnold says. These fees can range from 2% to 4% for each transaction, or a fixed-price transaction of 10 cents. They vary depending on the size of the purchase and type of card, says Craig Shearman, a spokesman for the National Retail Federation, so many retailers don’t accept credit cards on purchases on less than $10 and, sometimes, $5. “The extra dime becomes much more significant on a small transaction,” Shearman says. The economies of scale make it less profitable for a retailer to allow a charge of, say, 3 cents on a $1.50 pack of gum.

Bloomberg

Mortgages

Most mortgage lenders don’t let you put your mortgage payments on a credit card because they “don’t want you paying off debt with debt,” says Odysseas Papadimitriou, CEO of credit card comparison site CardHub.com. Consider: If you had your mortgage and credit card with one bank, you could end up getting into a ton of debt with that bank, which is risky for them; regulations prohibit banks from only letting people with credit cards from other banks pay their mortgage using the credit card, he adds. Furthermore, Papadimitriou says, they don’t want to have to pay the interchange fee, which is about 2% on average—especially in this low-rate environment.

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Auto loans

Many auto-loan lenders don’t let consumers pay their car loan using their credit card for the same reason they don’t let them pay their mortgage on one: they don’t want you paying off debt with more debt. But Papadimitriou says that there is a way around this in both instances—doing a balance transfer of the loan amount onto your credit card. He recommends that consumers be careful about this, though, because there are fees involved and credit card interest rates can be high. But if you find a 0% introductory interest offer and can pay off the balance transfer before it ends, it can save you money.

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College tuition

Whether or not you can pay your college tuition on a credit card depends on the school you go to and some don’t allow it, experts say. More often, though, the schools will allow you to pay with a credit card but charge you a fee to do it, says Mark Kantrowitz, the senior vice president and publisher of college resource site Edvisors.com. He adds that some credit card issuers don’t allow consumers to get rewards on their cards when they pay college tuition using their credit cards.

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Student loans

The U.S. Department of Education does not let you pay off your student loans using a credit card except in one instance: when you’ve defaulted on the federal loan, explains Kantrowitz. “But nothing stops you from taking a cash advance check from your credit card and paying the loan that way, though this isn’t advisable [due to how expensive it is],” he says. If you have private loans, it’s at the discretion of the lender whether or not they let you pay with a credit card.

See also: 6 amazing things you can do with credit cards