External Call Controller - Failed

Hello, I'm new using CI and I have a little problem.
 
I have development a website with Wordpress (landing page) and it don't have back-end functionallitys. My client wants to some functionality and I´m using CI to make it. The problem is following: 
 
From WordPress page (www.page.com) I want make a ajax request to a Controller_CI method (www.subdomain.page.com/controller/method) to validate login form and later redirect to web system (CI Project), but when I am making ajax request, I see this error in console and it don't make request:
 

Code:

XMLHttpRequest cannot load http://www.subdomain.page.com.ve/controller/method. No 'Access-Control-Allow-Origin'
header is present on the requested resource. Origin 'http://www.page.com.' is therefore not allowed access

 
I suspect that is cause by .htaccess file rules, but I don't know exactly. I don't want merge WordPress Page with Back-End functionality, so I created a subdomain (root folder CI) and separate it.

I hope can help me, thanks!

https://developer.mozilla.org/en-US/docs...gin_policy

https://developer.mozilla.org/en-US/docs...gin_policy

Thanks!