The 43-page affidavit was filed in connection with indictment of two US citizens, who did not register with Justice Department, as agents of Pakistan.
Fai is the director of the Kashmiri American Council, a Washington-based group that lobbies for self-determination for Kashmir. Its activities, the affidavit said, is funded by ISI. The money includes $100,000 given to political campaigns every year.
Foreign governments are prohibited from making donations to American political candidates.
"The investigation has led me to conclude that Fai has acted at the direction and with financial support of the Government of Pakistan for more than 20 years ... although Fai has some latitude to decide his day-to-day activities, the Government of Pakistan long has directed and funded his lobbying and public relations in the US," said Sarah Webb Linden, Special Agent, FBI.
The affidavit, filed before the US court on July 18 was made public after Fai was arrested.