The embassy did not disclose the reason for refusing Lawson, who admitted during a recent court case that she had occasionally used cocaine.
Embassy spokeswoman Lynne Platt said Thursday that Lawson was stopped from traveling Sunday and had subsequently been invited to the embassy to apply for a visa.
Lawson tweeted Saturday that she was going on vacation, but she also has worked in the U.S., where she co-hosted TV cooking competition "The Taste."
British citizens need visas to work in the U.S. but not for a vacation.
U.S. authorities may refuse passengers admission for various reasons, including drug use.
A spokesman for Lawson declined comment.