US District Judge Anthony Trenga found the women Muna Osman Jama, 36, of Reston, and Hinda Osman Dhirane, 46, of Kent, Washington guilty on most of the charges they faced on today after they waived their right to a jury trial.
Prosecutors say the women used the chat room to round up small contributions on behalf of al-Shabab.
The women did not deny their sympathies for al-Shabab. But their defense lawyers argued that the money they raised went to people who were not clearly defined members of al-Shabab.
The defense also raised First Amendment issues, saying their advocacy for al-Shabab should not be fodder for a criminal conviction.
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But the judge disagreed, and said in his ruling today that the two women were integral parts of al-Shabab's fundraising operations. And he rejected the First Amendment defense.
The judge ordered both women, who had been free on bond during the trial, taken into custody immediately. They could face sentences of 15 years when they are sentenced in January.
Al-Shabab, which has been linked to al-Qaida, claimed responsibility for terrorist attacks including the 2013 attack on the Westgate shopping mall in Kenya that killed 67 people.
Defense lawyer Alan Yamamoto argued that the women pose no threat, saying the money amounted to less than USD 5,000 over several years.