Is this controlling?

[Lolalocket]

OK I have name changed for this as the story is recognisable and I don't want my usual MN name to be outed.
My younger sister has been going out with a guy for about 2 years. They are both mid twenties and live together. The relationship is serious and I am expecting that they will get engaged in the next 6 months or so. There are no children.
Her boyfriend is a very affable, friendly lad. He is confident and very able to offer his opinions often interrupting and talking over people. My sister is quieter and more reserved than him. He has always appeared to me to be mad about my sister. In general my sister feels the relationship is good and they get on brilliantly, talk about everything etc.
There is one issue and it is making me uneasy as I am not sure if it is an indicator of things to come. He does not like her going out and drinking. He has no issue with her going out with her friends and having a couple of drinks but he has told her that if she goes out and gets pissed ever again without him being there he will break up with her.
She is by no way a messy drunk. She never does anything untoward and can always get herself home. She does not go out that much without him and when she does she rarely gets pissed (maybe a couple of times a year). He rings her when she is out or just after she gets back (she will usually stay at my folks after a night out) and he will decide form her voice if she is drunk or not. If she is there is an almighty row (lasting days) and after the latest incident he has issued this ultimatum.
My sister I think is tempted to accommadate his demands, while I feel this is a dangerous precedent. While there is nothing wrong in the aspiration never to get drunk again I believe it should come from her and not because he is threatening her. He is very black and white and qiute forceful in his opinions so I think she finds it hard to discuss things with him as he tends to talk her down. She says she feels like she is on tenterhooks now and its only a matter of time before she slips up.
So what do you think? Controlling or legitmate deal breaker from his pov?

My abusive ex didn't trust me because an ex of his apparently cheated on him. I would say he is testing the water and if she does as he says he will only get worse. My ex seemed friendly and funny too, to everyone else.
I don't like my partner drinking because of alcoholism in my family but I'd never check up on him, threaten to leave him or anything like that.

Without a doubt he is controlling, regardless of the reasons.
I know many who are "often interrupting and talking over people" and they're generally otherwise nice, well meaning, genuine people, but this in combination with trying to tell your sister what she can do is a red flag, I feel.
She should get in there first and initiate the split otherwise next it'll be rules about what she wears, where she goes, who she's with...

Thanks a million for your input everyone. I have found it really helpful. I am going to talk to my sister again about this. Ultimatly I suppose it is her call but I do think counselling for his insecurity/ trust issues would be a starting point.

Thanks again. I am changing back to my old name now so i won't be back on this thread.