"A special direction was considered and granted and subsequently her visa application was approved."
It is the first confirmation that Lawson, who has admitted using cocaine on several occasions, has been stopped from travelling to the US, where she presents a TV cooking show.
British media had speculated she had been barred, but Lawson had never confirmed it.
Last month, witnesses reported Lawson had been turned away from a British Airways flight to Los Angeles.
US law allows for people to be barred for drug use, even if they have not been charged.
The 54-year-old "domestic goddess" split from husband Charles Saatchi after images emerged of him grabbing her throat outside a London restaurant, and was then forced to admit drug use during the fraud trial of two assistants.
But the scandals haven't put Whittaker's off — this will be the second time the confectionary company has used the glamorous cook to promote its chocolate.
It is understood the new commercial will be filmed in Wellington early next month.
Auditions are reportedly being held for an advertisement that may include Lawson approaching people in the street and blindfolding them for chocolate taste tests.
Whittaker's declined to comment on Lawson's trip.
"We don't comment on our marketing strategy," said marketing manager Holly Whittaker.
"What I can say is that we have worked with Nigella, and she was a delight to work with."
At the height of the controversy, the company described its relationship with the star as positive, and sent her chocolates "to help her through the festive season".
"We chose Nigella because she is widely liked for her warm and refined manner," Holly Whittaker told the Herald on Sunday at the time.
"What happened is disappointing, but we are remaining neutral at this stage. What happens in Nigella's personal life is out of our control, but that is the risk you take when engaging with celebrities."
She said the company had received no complaints about Lawson, and 2000 customers posted messages of support on social media.
University of Canterbury associate professor of marketing, Ekant Veer, did not think using Lawson would have a negative effect on Whittaker's.
"A lot of Kiwis are quite forgiving. In the US, you couldn't do this — personal and public go hand in hand.
"Here, as long as she cooks well and is a nice person, we don't really care."