Some smugglers drive it across the border from Canada. Others sneak it through airports or send it in the mail, wrapping the contraband in T-shirts and towels to deceive the authorities. A few even make it at home.

But this is no international drug ring. It is the black market for Scottish haggis, a savory pudding of boiled sheep innards wrapped in a sheep’s stomach.

On Saturday, Scots across the world will dine on haggis to celebrate the birthday of Robert Burns, the 18th-century Scottish poet. But for haggis purists in the United States, celebrating Burns Night can be a challenge. Since the 1970s, the Department of Agriculture’s food-safety division has banned the sale of sheep lungs, which give traditional haggis its distinctive crumbly texture.

Many of the millions of Americans with Scottish ancestry have happily settled for an increasingly wide array of lung-less haggis (or, repulsed by the thought of eating sheep innards, avoided the dish entirely). For decades, however, a small but impassioned contingent has resorted to illicit methods to bring authentic haggis onto American soil, motivated by a commitment to tradition and a fondness for the taste and texture of boiled lung.