Shares closed down 10.84 percent at Aus$3.62, while the benchmark S&P/ASX200 slipped only 0.4 percent.
Earlier in the day Qantas shares had been down as much as 11.6 per cent, the biggest intraday fall in two years, Bloomberg News reported.
Qantas said softer demand, related to Australia's upcoming national election expected in early July and a recent drop in consumer confidence, had been seen since late March.
"In response to changed demand conditions, the Qantas Group has revised planned capacity additions in the final three months of financial year 2016," the airline said in a statement.
Qantas has also scrapped three Sydney-Los Angeles services since mid-April, redirecting capacity to Singapore and Hong Kong.
The Australian carrier in February announced that first-half net profit had soared 234 per cent on the back of belt-tightening and lower oil prices.
The bottom line was boosted by strong performances across almost all of the airline's divisions, with both domestic and international operations in profit.
