Former Rep. Mark Siljander (R-Mich.) pleaded guilty Wednesday to violating federal law for his role in helping an Islamic charity accused of financing terrorists.

Siljander, who was indicted in October 2008, pleaded guilty in the U.S. District Court for the Western District of Missouri to obstruction of justice and acting as an unregistered foreign agent in connection to his work for the Islamic American Relief Agency, based in Columbia, Mo.

The 59-year-old ex-lawmaker, who served in the House from 1981 to 1987, was charged with lying about whether he was lobbying the Senate Finance Committee to get the charity removed from a list of suspected terrorist organizations.

The charity paid Siljander for the advocacy work with $50,000 in funds that it allegedly stole from the U.S. Agency for International Development, according to the indictment.

Siljander later lied about the lobbying to federal investigators, telling them that the payments were charitable donations to support a book that he was writing about bridging the gap between Christianity and Islam, the indictment charges.

“A former congressman engaged in illegal lobbying for a charity suspected of funding international terrorism. He then used his own charities to hide the payments for his criminal activities,” U.S. Attorney Beth Phillips said in a statement Wednesday. “Siljander repeatedly lied to FBI agents and prosecutors investigating serious crimes related to national security. With today’s guilty pleas, all of the defendants in this case have admitted their guilt and will be held accountable for their actions.”

Siljander could face up to 15 years in prison and up to $500,000 in fines, according to the Justice Department.

Tory Newmyer contributed to this report.