Breaking shimmy

Hey, new here and need a little help. I'm getting a pretty bad shimmy/shake when I engage my breaks at a high speed. It doesn't so much do it when I'm going 25 - 30 mph but only when I engage the breaks going 45 and above. Some times it's worse than others. Someone told me that my rotors need to be turned. I had new tires put on two months ago and my breaks are fine. It's a 2006 model. Any info you could give would help.

Thanks