Cisco Systems's chief executive officer has written a letter to President Barack Obama urging him to curtail government surveillance after evidence circulated showing the National Security Agency had intercepted Cisco equipment, a company spokesman said on Sunday.

In a letter dated May 15, John Chambers, chief executive officer and chairman of the networking equipment giant, warned of an erosion of confidence in the U.S. technology industry and called for new "standards of conduct" in how the NSA conducts its surveillance.

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"We simply cannot operate this way, our customers trust us to be able to deliver to their doorsteps products that meet the highest standards of integrity and security," Chambers said in the letter.