A Portland woman pleaded guilty Tuesday in U.S. District Court in Bangor to sending bomb threats through the mail to religious congregations in California, U.S. Attorney Halsey B. Frank said.

Nina Michalski, 61, faces up to 10 years in prison, a $250,000 fine and three years of supervised release, Frank said in a statement. She will be sentenced at a later date.

Frank said Michalski mailed three letters between October 2016 and February 2017 that indicated a bomb had been planted or would be planted at the congregations’ facilities.