Jewish cooks across the US have been left distraught after a popular brand of chocolate chips was stripped of its "parev" label.

The Trader Joe's semisweet chocolate chips have long been a staple of the kosher kitchen, with people using them to whip up all manner of milk-free desserts.

But due to a change in the factory equipment last month for cost-cutting purposes, the product is no longer certified as kosher. Although the recipe is the same, a spokeswoman for the company explained that after the cleaning process used was altered recently, Trader Joe's was compelled by the Food and Drug Administration to label bags with a warning about milk allergies, thus affecting the product's parev status.

Shoppers have reacted to the news by seizing any packets that still have the old label, with one customer in Chelsea, New York, buying 90 bags on one visit.

Rabbi Chaim Fogelman, of the kosher supervisor OK Kosher, said: "As much as everybody wants us to label these parev, under no circumstances would we want to label something parev when we have a hunch there might be a dairy chip in the bag."

More than 4,600 people have signed an online petition calling for the change to be reversed.

"Many of us rely on their being parev - and not dairy or dairy-equipment - to meet our dietary needs," the petition reads.

Shulamis Labkowski, a Jewish mother from California, told the Wall Street Journal: "I'm hoping once they realise the significance to such a large amount of people, they'll reconsider."

"They are so delicious the way they are - why would you want to change the recipe?" asked signatory Zippoirah Freedman.

Another woman added: "Keeping kosher is so much more enjoyable with Trader Joe's chips. We beg of you, have mercy, and keep our chips parev."