The council voted 6-2 to replace Hicks with Councilman Danny Scarth during Tuesday night's meeting.
Hicks said she was blindsided by the decision to vote on the post and heard about it first through the media.
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Hicks has held the position since 2006, and her supporters claim that her removal comes as punishment for taking positions at odds with Mayor Mike Moncrief and other council members, the Star Telegram reported.
The council began voting annually on the mayor pro tem in 2006, but did not vote last year, the city's spokesman Bill Begley told the paper.