The a2 Milk Company has spurned a complaint about its product in the United States and has vowed to keep on promoting its milk there.
It has said a challenge that has been referred to the Federal Trade Commission is based on incomplete and outdated scientific evidence.
a2MC markets a milk product without a protein that it says some people find hard to process.
The company, which is listed on the New Zealand Stock Exchange, sells products mainly here, and in Australia and China.
But it has been pushing its milk into the US, with the slogans, Easier on digestion and "May help some avoid discomfort".
This led the US dairy lobby group, the National Milk Producers Federation, to complain that a2MC was making false claims based on an unreliable and clinically insignificant study.
The federation also complained that a2MC falsely said that conventional milk was likely to induce "painful bloating, wind, cramps, gut inflammation" and other uncomfortable symptoms.
A complaint was then filed with a self-regulating forum run by the US advertising industry, the National Advertising Division, alleging the ads breached standards of truth and accuracy.
a2MC's marketers replied the scientific evidence produced by the Federation was itself incomplete and outdated, and a2MC had been exonerated by a separate case in California.
After considering the matter, the National Advertising Division said it acknowledged the position of a2MC, but noted that the company had declined to participate in a review of its advertising claims.
As a result, it was referring the matter to the Federal Trade Commission for further review.
The company in New Zealand has rebutted the claims made against it and vowed to fight on.
"We were disappointed, but not surprised, to learn that a challenge was filed by our conventional milk competitors," a2MC said in a statement.
"The challenge was unfounded and there has been no finding of any wrongdoing by the a2 Milk Company.
"While the a2 Milk Company supports industry self-regulation, the primary issues in the challenge had previously undergone extensive regulatory review.
"We strongly believe in truthful advertising and we will continue to market our products accordingly."