A number of Rangers fans tore up seats and clashed with security inside the Romanian team's Steaua Stadium.
Rangers chief executive Martin Bain said in a statement that some supporters had complained of being sprayed in the face with CS gas and treated heavy-handedly during the 1-1 draw.
The Scottish champions said the problems arose after fans were led into the stadium through two turnstiles when access to four had previously been arranged.
"Obviously the behaviour of some of the fans inside the stadium was unacceptable and no-one likes to see that," Bains said on Rangers website.
"However, what was equally unacceptable was the fact that Rangers came to this stadium with representatives from UEFA and Unirea a number of weeks ago and arranged for the four turnstiles to be open to give access to our supporters.
"When they arrived this evening there were only two turnstiles open which caused difficulty gaining access and fans then to be sprayed with CS gas is totally unacceptable.
"I will now make a representation to UEFA in their behalf."
Bucharest police described the incidents within the ground as minor and said they did not have to intervene during the match.
