The six men and one woman entered the guilty pleas Wednesday, paving the way for a swift judgment in August.
They had been indicted by a federal grand jury in Los Angeles in 2001 on charges of providing funds to the Iranian opposition group Mujahedin-e Khalq, or MEK.
The charges carry a maximum penalty of 20 years in prison.
But after the eight-year legal battle, the American Civil Liberties Union said the group made the guilty plea agreement to enable them to head straight for an appeals court "on the grounds that their prosecution violates the US Constitution."
The group's challenge "focuses on the fact that the MEK does not threaten US national security, in large part because the US government has itself provided material support to the same group, as court documents obtained in the case revealed," the ACLU said in a statement.
As part of their guilty plea, an agreement was made that the government would drop over 100 charges, to which the seven have pleaded not guilty, the ACLU said.
The accused admitted in court to raising funds for the MEK from supporters and others at public places like the Los Angeles International Airport.
The MEK was designated a foreign terrorist organization by the United States in 1997.
Opponents of Iran's Islamic Republic, the MEK carried out operations against the clerical regime in Tehran from Iraq, under the protection of former president Saddam Hussein.
