With MerrillEdge, if your shares are in a margin account, they can be borrowed. If your shares are in a cash account, then they cannot be borrowed. YMMV I had 165000 shares in a margin account and had to keep a gtc order open which was a pain because of the share quantity. MerrillEdge wasn't too keen on my putting a gtc sell on so many shares. I ended up moving all my shares to a cash account.