IndyMac Bancorp. is laying off 400 employees, or about 4 percent of the lender’s total work force. The layoffs are effective immediately.

IndyMac’s Chief Executive Michael Perry sent an e-mail to employees announcing the news, the Pasadena Star News reported Friday. The paper said most of the affected workers are in the bank’s Operations and Enterprise Process & Technology groups, which have offices around the country.

Perry said in the e-mail sent Thursday that the layoffs were needed “to protect our business and remain competitive.”

An IndyMac spokesperson told the Star News that the layoffs were not fueled by the subprime slide but were largely the result of the overall slowdown in the nation’s housing market.

The layoffs will essentially return the company’s staffing to where it was earlier this year, according to IndyMac.

Shares in IndyMac lost 52 cents to $26.75 in afternoon trading Friday on the New York Stock Exchange.