[cnn-photo-caption image= http://i2.cdn.turner.com/cnn/2010/images/09/17/art.murkowski.0916.cnn.jpg caption ="Sen. Lisa Murkowski will announce her plans to run as a write-in candidate Friday."]
(CNN) - When Sen. Lisa Murkowski of Alaska announces Friday night - as expected - that she is launching a write-in campaign to retain her seat, she'll be stepping into the middle of some very testy Republican infighting.
Tea Party Express Chairwoman Amy Kremer, whose group campaigned heavily for Murkowski's primary opponent - and eventual primary winner - Joe Miller, said the senator's decision proves she doesn't "get it."
"She was fired by the people. The people were given a choice and they voted for somebody else," she said, adding that she was shocked to learn of Murkowski's decision.
A Republican source told CNN that Murkowski informed "a few" close colleagues that she plans to run as a write-in candidate. A separate source with knowledge of her decision said she expects to announce her write-in candidacy Friday.
Updated 8:45 p.m.