Automatic Transmission jumps to low gear

Just looking for a little help! I am having a problem with my transmission jumping into low gear. The transmission runs ok first think in the morning but as I drive to work and the car begins to warm up the issue happens. I will be driving on the highway and get up to speed but as I slow down to first gear the transmission will jump to low gear. Once it is there I cannot get it out of low gear until I put my car in park and the turn off the engine and then restart the engine.