Myer has posted its biggest interim profit fall since going public in 2009.
The shock announcement comes after it confirmed it would meet full-year earnings just two weeks ago.
Myer reported a 23.1 per cent fall in half year profit to $62.15 million.
Earnings before interest and tax (EBIT) for the period was down 20.8 per cent to $100.2 million.
Full-year guidance has now been lowered to between $75 million and $80 million, excluding one-off costs.
First half total sales were up 1.5 per cent to $1.8 billion, up 0.9 per cent on a comparable store sales basis.
January sales were also up 3.9 per cent.
However, the cash cost of doing business over the half year was up 6.2 per cent to $569.6 million.
Myer expects total costs to grow by approximately $15 million in the second half compared to second half of fiscal 2014.