HTML TAGs disappears

On my blog there are several editors.

The problem is that publishers do not manage to save some HTML tags.

Example:

<iframe src = "https://www.google.com/calendar/embed?
mode=AGENDA&height=600&wkst=1&bgcolor =% 23999999
& src = adolescentesidg% 40gmail.com & color =% 235A6986
& ctz = America% 2FSao_Paulo"
style = "border: solid 1px # 777 "width =" 800 "height =" 600 "
frameborder =" 0 "scrolling ="no"> </ iframe>

When they publish this code it disappears.

Only I, as administrator, can post this type of content.

Is there a way to give privilege to all users who are not administrators to post this kind of tag?

Grateful