The class action alleges that a2 Milk engaged in misleading or deceptive conduct in breach of the Corporations Act.
The company is also accused of breaching continuous disclosure rules in posting four downgrades on September 28 and December 18 last year, and February 25 and May 10 of this year.
In a statement, a2 Milk said it had been notified that group proceedings have been filed.
"The company considers that it has at all times complied with its disclosure obligations, denies any liability and will vigorously defend the proceedings," it said.
"The company remains confident in the underlying fundamentals of the business and growth potential," it said.
The market took a dim view of some big share sales by certain directors and executives when the stock was just shy of its peak late last year. There is no suggestion that any of those share sales are connected to the legal action filed by Slater & Gordon.
The share sales took place within the allowable "window" after the company's result.
Slater and Gordon's Kaitlin Ferris said a2 Milk "was or ought to have been aware that the full-year FY21 guidance did not adequately consider factors likely to impact the Company's financial performance".
It is also alleged that a2 Milk's sales in the CBEC channel would in turn be impeded by the
disruption to the daigou/reseller channel and the loss of associated marketing activity to
stimulate consumer demand.
"As a result of our investigation following a2's profit downgrades throughout FY21, we
concluded that there was a strong basis to allege that the company provided misleading
guidance and was obliged to correct the market's understanding of its financial position at a much earlier time," Ms Ferris said.
