Tuesday night, Shannon Funk was returning to Long Beach Airport in California from a trip to Manhattan when she was served the subpoena by Aaron Cohen, a former Israeli intelligence officer who now runs IMS Security in Los Angeles.
Within the next few weeks, Funk will have to sit for questioning by Federline's lawyer, Mark Vincent Kaplan, OK! reports.
Funk no longer works for Spears, but that hasn't affected her loyalty to the former teen queen.
"What can I do about this?" Shannon asked regarding the papers. "Is this a big deal? But honestly I have nothing negative to say about Britney, so let Kaplan go after me. I'm on Team Britney! I support her no matter what. Kevin's a bad father."
Meanwhile, the same night she reportedly locked lips with college student Matt Encinias, OK! reports that a topless Spears nuzzled up to Funk.
“Instead of hooking up with him, [Shannon] ended up back in Brit’s room and bed,” a source told OK!
The magazine's cover shows the two women topless in a pool together, with Funk kissing Spears on the cheek.
Another assistant to Spears, Alli Sims, was also subpoenaed on Sunday.
Spears' divorce from rapper and dancer Federline became official July 30.
Since February, Spears, 25, and Federline, 29, have shared joint custody of their sons, 22-month-old Sean Preston and 10-month-old Jayden James. Federline is seeking additional custodial time.