The head of the CIA has told its employees that they must not "identify with, support or champion opposition" to the Bush administration.
New CIA director Porter Goss is proving controversial
The email to staff by Director Porter Goss, a former Republican congressman, has been seized on by critics.
They say he is trying to undermine the agency's political independence, but the White House denies this.
Several leaks of intelligence relating to Iraq occurred during the recent US election campaign.
Much of it was embarrassing the administration, leading Republicans to say elements within the spy agency were siding with the opposition Democrats.
The email, which was itself leaked to several US newspapers, comes after two top CIA officials resigned amid reported disagreements with the new leadership of the agency.
Deputy Director for operations Stephen Kappes and his assistant Michael Sulick were part of the CIA unit dealing with covert operations around the world.
Mr Goss' email, which was itself leaked to several US newspapers, said: "We support the administration and its policies in our work.
"As agency employees we do not identify with, support, or
champion opposition to the administration or its policies.
"We do not make policy, though we do inform those who
make it. We avoid political involvement, especially
provide the intelligence as we see it - and let the facts
alone speak to the policymaker."
It also reminded CIA employees of their "oath of secrecy".
It added that communication with the media should be carried out via the CIA's public
affairs office, while any contacts with Congress should be through
its office of congressional affairs.
Democratic Senator Dianne Feinstein, a
member of the Senate Intelligence Committee, said the email was not "even-handed".
She added: "As I look at the intelligence community, it should not
support or oppose an administration.
"It should be
professional, factual and give the best possible analysis
regardless of where the chips may fall."
White House spokesman Scott McClellan said some people had
"misconstrued" the email.
"He was not talking about advocacy one way
or the other."
Mr Goss, who took office two months ago, has been given a
mandate to reform the agency in the wake of intelligence failures on
Iraq and the 11 September 2001 attacks on the US.
For the previous seven years, the CIA was led by George Tenet, a Clinton administration appointee who stayed
on through most of Mr Bush's first term.
Before he was nominated to run the CIA, Mr Goss said he thought the agency had failed in its "core mission".