Microsoft is trying to push Windows 10 by all means.
It's a good thing if you are a home user and get a free upgrade.
But it is just opposite in corporate environment, where every business app and device needs to be tested before rolling out changes and especially an OS upgrade.
Here is a Microsoft KB article, which describes how to manage Windows 10 Upgrade notifications https://support.microsoft.com/en-us/kb/3080351
In short - you can disable upgrade notifications in two ways:
1) Use this group policy setting Computer Configuration / Administrative Templates / Windows Components / Windows Update Policy / Turn off the upgrade to the latest version of Windows through Windows Update
2) Deploy this registry value: