The lawmakers warned that the decision "could, among other things, have a chilling effect on the work of the intelligence community" because of fears among agents of possible future prosecution.
Republican Senators Jon Kyl, the party's number two in the Senate; Kit Bond, co-chairman of the Senate Intelligence Committee; and Jeff Sessions, the ranking member of the Senate Judiciary Committee were among the nine signers.
"Despite your assurances that this investigation will be narrow and focused, there is a real risk that today’s announcement portends a long, arduous, and unpredictable process for the intelligence community," they warned.
"By delegating the prosecutorial function to a largely unchecked special prosecutor, you are responsible for having set a course that may diminish our intelligence efforts," said the senators.
The same lawmakers wrote Holder on August 19 to urge him not to open an investigation into alleged CIA abuses.
Earlier, Holder announced he was naming a career prosecutor, John Durham, to open a review to determine whether there was evidence that laws were broken in CIA interrogations at secret sites overseas.
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