Delta earnings forecast falls short of Wall Street estimates, shares down 10%.

CHICAGO (Reuters) -Delta Air Lines forecast lower profits in the third quarter than analysts had expected, with the carrier citing discounting pressure in the low end of the market, sending the company’s shares down about 10% before the bell on Thursday.

The Atlanta-based carrier also reported a hit to transatlantic bookings as travelers are avoiding Paris due to the Olympic Games this summer.

Delta shares were trading at $42.38, while rivals United Airlines and American Airlines (NASDAQ: AAL) were down 4% each.

Domestic peer Southwest Airlines (NYSE: LUV) was also down 3%, while European rivals Lufthansa and British Airways owner IAG fell between 1% and 2%.

Delta forecast an adjusted profit between $1.70 and $2.00 per share in the third quarter through September compared with analysts’ expectations of $2.05, according to LSEG data.

Airlines are enjoying a summer travel boom, with more than 3 million people passing through U.S. airport security checkpoints in a single day on July 7.

The boom has failed to lift earnings at most of the U.S. carriers as excess industry capacity has undermined pricing power. Major airlines have scheduled about 6% more seats in the domestic market this month than a year earlier, data from consultancy Cirium shows.

It is having a dampening effect on airline fares. Average round-trip ticket price for a U.S. domestic flight was $543 in May, down 1% month-on-month and 3% lower from a year earlier, according to data from Airlines Reporting Corporation (ARC).

American Airlines and Southwest have cut their revenue forecasts in the second quarter, citing discounting pressure.