The US regulator detailed its concerns about the plant in Horsholm in a untitled letter last week, accusing ALK of failing to establish procedures to prevent microbial contamination or test anti-allergy products made at the site.
According to the agency, ALK has also failed to routinely recalibrate some equipment.
FDA uses Untitled Letters for violations that are not as significant as those that trigger warning letters.
Unlike a Warning Letter, an Untitled Letter does not include a statement warning that failure to promptly correct a violation may result in an enforcement action.
It cited an instance when the firm abandoned a batch of the venom-based allergy treatment Pharmalgen due a faulty lyophilizer as an example of the problems caused.
The FDA said that ALKs response was insufficient and lacking in detail, explaining that “in many of your responses you simply indicate that the written procedures will be updated and training will be improved.”
The agency also said: “further information and discussion with [ALK] will be necessary to adequately review and assess [its] planned actions.”
It also pointed out that some of the compliance problems seen at Horsholm were also observed at ALK’s manufacturing site in Port Washington, New York, US during an inspection conducted in 2014.
ALK generated revenue of DKK151m ($22m) in North America in 2015, roughly 18% of its total revenue for the year.
A spokesman for the firm told us: "ALK received an Untitled Letter from the FDA regarding an inspection of ALK’s production facility which took place in March 2016" adding that "ALK is in open dialogue with the FDA to resolve the issue and expects to submit additional formal responses very soon.
He went on to say that: "The letter mainly relates to the product Pharmalgen, an allergy immunotherapy for bee and wasp sting allergies, which is produced at the Hørsholm facility. Other products for the American market produced at the Hørsholm facility are Ragwitek and Grastek."