How can I open Modal Popup from code behind

I have a page that on load builds a datatable base on the users userid.

An if else statment detemrines whetehr or not the user simply proceeds or else has to make a selection prior to proceeding.

So there is no control to open the modal popup from like a button click...and whats more not EVERY person accessing the window will get the modal popup.

I assume there is a way in the code behind that I can fire up the Modal Popup as a condition of the else...

any help would be appreciated.

Call the show method.

ModalPopupExtender1.show()