Was looking this up online without success after an incident on an international flight and was wondering if you guys had any more information. I was in business class and my husband was in coach (another issue that I won't delve into) and I went back there after we were in the air to give him sleeping medications for the 10+ hour flight--was very rudely told by coach cabin flight attendant that I was a security risk and was not allowed to move between cabins. I asked why and she just kept repeating security risk angrily and I went back to my seat and asked the flight attendant in the business class cabin who said it was fine to go to the coach cabin but that he can't come up (which I understand). Is there a set rule that I can see online (and reasoning) because I'm quite confused.