The Air Transport Association made the forecast Monday despite deep discounting by airlines over the past several months.
"It is increasingly apparent that the economic head winds facing the airlines and their customers are anything but behind us," said James C. May, the group's president and CEO. He said the unemployment rate jumping above 10 percent last month has affected consumer buying decisions.
U.S. airlines have struggled this year with declining traffic during the recession. They cut fares for the peak summer vacation season and have eliminated many unprofitable flights to save money.
With fewer flights, planes are likely to be full over Thanksgiving, the trade group said. It called the capacity reductions the deepest since 1942.
The group said the four busiest travel days around Thanksgiving are expected to be Monday, Nov. 30; Sunday, Nov. 29; Friday, Nov. 20; and Wednesday, Nov. 25, the day before the holiday.
The group said passengers should pack light, check the status of their flight before going to the airport, and get to the airport early.