Yes, as soon as you breach the contract by missing a single payment - they can put an immediate call on all debt you owe. That goes for Credit Cards, that goes for a promissory note from your uncle, that goes for anyone that you have a binding debt contract with.... usually, as with anything there's always exceptions. And even if they're legally allowed to call your debt when you miss a payment - realistically, they'll probably work with you because it's cheaper in the long run to reduce your rate and let you pay than to take you to court over it. But, your credit score will take a beating.