(Reuters) -A travel association has urged the U.S. Congress in a letter on Monday to reopen the federal government ahead of the Thanksgiving travel rush, as the shutdown stretches into its 34th day.

The prolonged shutdown has led to a spike in airline delays, affecting airports and 3.2 million passengers due to a high number of absences in air traffic controllers, with many of them taking up second jobs to cope.

The shutdown is estimated to cost the U.S. economy between $7 billion and $14 billion, according to the nonpartisan Congressional Budget Office.

"Air travel's number one priority is safety and while safety will be maintained, travelers will pay a heavy and completely unnecessary price in terms of delays, cancellations and lost confidence in the air travel experience," said U.S. Travel Association President and CEO Geoff Freeman. 

In a letter that was signed by 500 organizations, including Hilton and MGM Resorts, Freeman urged the Congress that the fastest way to restore confidence and restart travel was to reopen the government by passing a clean continuing resolution.

"The damage from this shutdown is growing by the hour with 60% of Americans reconsidering their travel plans".

The shutdown has forced 13,000 air traffic controllers and 50,000 Transportation Security Administration officers to work without pay and snarled tens of thousands of flights.