Credit card companies probably didn't know it would come to this when California passed proposition 215 in 1996 legalizing medical marijuana. But the major cards are faced with a decision: Can you pay for weed with plastic or not? As it turns out, mostly yes.

According to a report on Credit.com, Visa and Discover both allow purchases at medical marijuana dispensaries, which are becoming increasingly commonplace nationwide. MasterCard has allowed such purchases in the past but it's reconsidering its policy at the moment and isn't quite sure what it will decide on. American Express is the prude here, with a staunch no-pot policy. "It is our policy to adhere to the federal law in such matters," spokesman Bradley Minor said. Federal law still deems marijuana illegal, even if states legalize it.

AmEx may want to reconsider its position as opportunities to buy pot with your credit card become more and more plentiful. Last month, Delaware became the 16th state to legalize marijuana, and ten others have legislation in the works to do the same. In Arizona, which recently sued the federal government over its own medical marijuana law, a new pot-supply superstore that Gawker has dubbed the Wal-Mart of weed, opened in Phoenix yesterday.