The guard at the McDonald's outlet on Seven Sister's road in Holloway asked the girl to take off the hijab if she wanted to queue up for ordering food, The Independent reported.
"It's just a matter of taking it (hijab) off," the guard told the girl. She responded, "It's not just a matter of taking it off. I wear this for religious reasons and I'm not ashamed of it, and I will stand in line and I will get the food I want, because this isn't okay."
Another customer, a British Muslim of Middle Eastern descent, intervened to defend the girl but was told by the guard, "It's none of your business."
The restaurant later issued an apology and said it has suspended the security guard involved in the incident.
In a statement, McDonald's said it has no policy which restricts or prevents anyone wearing a hijab, or any other religious attire, from entering their restaurants.
"We welcome customers of all faiths and sincerely apologise for this situation. We are taking this matter very seriously and are addressing the situation with the individuals involved; the security guard, from a third party company, has been suspended," the statement read.