Bankers and traders at Lehman Brothers Holdings Inc. will be dragging their suits out of storage, as the venerable investment bank is abandoning its flexible dress policy, according to an internal memo.

The more casual policy -- introduced three years ago -- gave employees the option of wearing business attire or less formal clothing, with the understanding that employees dealing face-to-face with clients would dress appropriately.

Now, men working at Lehman will have to wear suits and ties, while women will be required to don either skirts, pants, dresses, or "other equivalent attire," the company's operating committee said in a note sent to employees on Tuesday. The new policy goes into effect on March 11.

"As Lehman Brothers has grown over the past few years, the amount of client contact at the firm has increased significantly and should continue to do so," the memo said.

A Lehman spokesman declined to comment on the memo.

The Internet boom of the late 1990s enticed many potential investment bank employees to work at dot-coms, lured away by the promise of lucrative stock options and a more casual work environment.

Even the most staid Wall Street firms loosened their dress policies to keep pace with the dot-commers, but when many Internet companies crashed and left thousands out of work, banking again became an attractive option for top talent.

Many other securities firms may adopt Lehman's stricter policy, but so far casual is still in vogue.

Credit Suisse First Boston, the investment banking unit of Swiss financial services giant Credit Suisse Group , is still business casual, a spokeswoman said.

A spokesman for Citigroup Inc. unit Salomon Smith Barney said business casual dress is still allowed. Morgan Stanley and Merrill Lynch & Co. Inc. officials could not be reached for comment.

Lehman staff in offices where client visits are uncommon can still wear more casual clothing, the memo said.

And the other employees shouldn't ditch those khakis and golf shirts just yet -- casual dress will be allowed on Fridays during the summer months.