Saudi Arabia first suggested the idea in December, CNN said.
The Gulf Cooperation Council was formed in 1981 by Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates.
Saudi Foreign Minister Saud al-Faisal has said shifting to a union would help protect group members from outside threats. Analysts say Iran is a particular concern in the face of strengthening ties between Iran and Iraq, CNN reported Monday.
Bahrain has blamed Iran for fueling anti-government unrest.
Khalid bin Ahmed al-Khalifa, Bahrain's foreign minister, said a union of Gulf nations " shall fortify the GCC against any external threats or irresponsible acts, especially in light of the significant changes the world is witnessing," the Bahrain News Agency said.
Qatar, and possibly Kuwait, are expected to announce their intentions to join the union, al-Hayat newspaper reported.
An al-Hayat source said the United Arab Emirates and Oman would join at a later stage.