Twice as many U.S. companies than previously expected are cutting their travel spending this year in response to economic weakness and uncertainty.

The Association of Corporate Travel Executives says 71 percent of its member companies now plan to spend less on travel this year than in 2008. That's a huge and unprecedented shift in corporate travel managers' plans just five months ago, says Susan Gurley, the association's executive director.

In September, when the association asked about travel spending plans, only 33 percent of respondents said they expected to cut back. In fact, 36 percent said they would be spending more on travel in 2009.

But in the just-completed survey, only 8 percent of the ACTE member companies that responded said they now expect to spend more on travel this year.

Most companies are seeking to spend 10 percent to 20 percent less on travel than they were expecting to spend just five months ago, the latest survey shows. Using the most conservative figures for estimating the dollar impact of such cuts, the ACTE suggests that the 176 member companies that responded collectively will spend about $880 million less on travel this year than they had planned.

If the same method for estimating is applied to the ACTE's full membership — about 2,400 companies — the impact would be more than $2 billion in foregone travel spending this year, Gurley says.

Never have corporate spending plans deteriorated this much, or this fast, she says.

"Not even after 9/11," she says. "And I don't think ... that it has bottomed out yet."

One reason: rising unemployment. If jobs are cut, companies are reluctant to approve travel.

"There's only two things that companies have immediate control over when the economy turns bad: personnel and travel," she says. "That's why we believe that as long as joblessness is still on the rise, travel spending won't begin to bounce back."