Either your rules are not clear or your safety culture is down.
What are you correcting?
Well, whatever way you go you have a job to do. Either your procedures are no good, or the groupdynamic is no good, or both, so there is work to do.
When it comes to the procedures, it is important to have procedures in place that are aimed at helping professionals do their job safely and efficiently. Poor procedures, which are often drawn up by people who do not understand operations and are justified by a desire to control behaviour, are unacceptable and will actively invite violations. It is the duty of management to have good procedures in place. If safe working necessiaties a loss in efficiency, make sure this is understood and agreed so that it is done consciously.
When it comes to the safety culture, the most important thing to address is this: "In what way do people get pulled into not following the rules, and what keeps them there?". How does the "Code of Silence" work. Very often, this is how a negative culture builds:
Somebody does something, like not following a rule or procedure, and rather than correcting his or her behavior to rectify this, he or she exerts pressure on people to do the same. It might be that the person not following the rules is a seasoned hand, and rather than admitting his mistake he uses his authority to let people know that "people with experience can do this". If the other person buys into this, and says nothing, essentially a "secret agreement" is made to work this way. After a while, if enough people are into this game, the peer pressure will automatically draw other people in this game as well, and it becomes normal behavior - a culture.
How are you correcting?
To correct procedures: own up that the procedures are bad, and invite your best experts to correct them with you, bringing them in line with professional standards. If that is not possible immediately, due to e.g. the fact that the procedures were imposed from outside, openly address this issue and seek agreement on how to deal with this. Not dealing with bad procedures will lead to a bad safety culture.
To correct the culture: Well, there are many texts, approaches and books out there to help you. The most important thing is however that you start addressing the basics of the team behaviour ("Are we here to help each other excel?" and "How have we been working lately that is not in line with how we want to work?") and to bring the team back to the shared ambition and task of the whole team (in HRO's this is often related to caring for the lives of people).