Yes they can do this, and yes many on this board have reported this. Times are tough right now and banks are keeping a closer eye on accounts and taking action if they feel there is any risk to them. Even though there is no problem with THIS account, they are watching your credit in general. If you have higher utility on even one other account, that is enough to cause panic and for them to react. Unfortunately, there are a number of things that can cause this to happen. Higher UTL only being an example.
The best thing you can do is to continue paying on time and hope they will raise your line back up once our economy isn't in the situation it is in now.