Logos, most especially those used by corporations , associations or private entities are COPYRIGHT . This means they are the sole owners of the logo and are the only ones who could use it. They can, however, allow other people or entities to use the logo but by written permission.
If you use such a logo without asking permission from them, you are violating their rights as the sole owner and you are liable for it. They can sue you for that.
For more details about copyright infringement....
http://en.wikipedia.org/wiki/Copyright_infringement
..... Just to add, the forum is very strict with regards to COPYRIGHT. And this is something you have to learn, be careful with and practice in your day to day dealings as a freelance designer.