Gov. Christie says he would "crack down" on states that have legalized marijuana if he were elected president.
Under federal law, marijuana is classified as an illegal Schedule I drug. But in recent years, Colorado and Washington legalized the sale and possession of pot for recreational use. The states collect taxes on sales.
The Obama administration has taken a hands-off approach in those states, allowing them to experiment with legalization.
Asked by conservative radio show host Hugh Hewitt on Tuesday if he would change course and enforce federal law, Christie said, "Absolutely."
"I will crack down and not permit it," he said. "Marijuana is a gateway drug. We have an enormous addiction problem in this country.
"We need to send very clear leadership from the White House on down to federal law enforcement: Marijuana is an illegal drug under federal law, and the states should not be permitted to sell it and profit from it."
Christie, a Republican, traveled to New Hampshire this week and says he'll decide whether to run for president in 2016 by early summer.