Fed officials often think of the macro-economy in terms of the Phillip’s Curve trade-off between unemployment and inflation. (Officially, they refer to their “dual mandate” to fight both unemployment and inflation.) When an expansion progresses to the point at which labor markets tighten, the fear of cost-push inflation arises.
Here is Janet Yellen in 2015 on Fed tightening:
http://www.federalreserve.gov/newsevents/speech/yellen20150327a.htm
