Aon Hewitt, which tracks the accounts of 4.7 million workers, said the volume of money moved from stocks to fixed-income funds since last Monday was at the third-highest level since it began tracking data in 1997.
The volume of assets traded on Thursday exceeded $900 million. On a typical day, around $300 million to $400 million is traded in the 401(k) accounts Aon Hewitt tracks.
Volume remained high on Monday, reaching $862 million as Congress moved closer to reaching a compromise.
Last week, 95 percent of the assets moved from stocks to fixed-income investments, primarily stable value funds.
The trends show that workers, many burned in the last economic downturn and stock market meltdown, have little patience for leaving their money vulnerable again.
It was not unusual for 401(k) accounts to lose a third of their balance as the market plunged in 2008 and hit bottom in March of 2009.
"More fear and uncertainty had folks running to the sidelines rather than wanting to weather another one of those downturns," said Pam Hess, Aon Hewitt's director of retirement research.
After the market bottomed in 2009, about 6 percent of 401(k) assets in the accounts Aon Hewitt monitors moved from stocks to bond funds. Average stock exposure declined from about 70 percent to 50 percent of the assets, Hess said.
Only about 1 percent of those assets moved back into stocks, which means many investors lost out on the market's rise. The S&P 500 has nearly doubled since early 2009.
In the last few weeks about another 1 percent of assets has been moved from stocks.
Hess said the investors getting out of the market now will have a difficult time getting back in at the opportune moment to maximize their investment.
"It really is counterproductive," she said. "If you're focusing on the long term, reacting to short-term fluctuations is generally going to lead to suboptimal results."