Can becoming pregnant cause milk supply to decrease?

I got pregnant while I was nursing my first...and it did decrease a little bit. I was told by a friend to try this tea... its called MOTHERS MILK.... you drink it 3 times a day... its all herbal (so it wont bother your little one, I checked it out with my doctor before I drank it). My milk came back in really really well. I was getting 2 eight ounce bottles pumped in one setting. It was amazing. So to answer your question...YES your milk could possibly decrease if you were to be pregnant. But if you arent and its just decreasing then maybe you should look into something like the tea just to help get you back to where you need to be!