Premier Investments has called on the Myer Board to "urgently" release its first quarter 2019 results.
The company, Myer's largest shareholder, claimed Myer shares are trading on an uninformed basis.
Premier said it is considering legal and other regulatory options to ensure shares are being "traded in a fully informed share market."
Myer shares are currently trading at 46 cents, down from just under 80 cents last tear.
Premier said the Myer Board has indicated it will not be providing quarterly sales numbers at its upcoming AGM, where shareholders are being requested to vote for the board.
"How can Myer shareholders be kept in the dark ahead of a crucial vote?" Premier asked in a statement.
"Premier therefore calls for Myer to release its first quarter 2018 results by 1 November 2018 so that shareholders can make their own decisions."