I understand your situation.
You need to make them accept your presence in the office. Instead of talking to the aggressive employees, first allow them to talk and listen to them. You will for sure get a clear idea about what is running in their minds when you allow them to speak. Listening to others is indeed a difficult task.
Formulate your policies in line with the goals of the organisation, explain the benefits of adopting to the new methods to the employees very carefully. When the going gets tough, tough gets going.
If any employee is getting aggressive,first try to hear him out and understand what he wants to convey.
In anger the real message may be lost.
Secondly misplaced understanding of policy can cause a person to be angry.
One thing is always remain cool and tackle situation calmly.
Involvement of HODs and top brass will indicate that is company policy and not your policy.
One cannot keep everyone happy and there will always be some people who are affected by change and react adversely.
Whenever some employee reacts extra aggressively make it a point to inform his HOD and your HOD.
Many people do not like changes and get used to set way of working and resistance is natural.
Once people realise that this change is for good,uniformity and overall company good ,they will see reason and fall in line.
Those who still remain aggressive and out of control can be dealt with by counselling from HOD and/or disciplinary manner,if it so requires(Last Resort)
There are two very effective responses shared and I would urge you to implement the suggestions shared by them.
I would like to add the following
Do not make piecemeal changes. This means that you must study the entire system and make all the changes you propose in one go. Obviously most of the changes you propose would be focused on getting more productivity and this would mean tightening the system and possibly curbing the lax behavior of employees. If you make piecemeal changes existing employees, rightly or wrongly, are bound to get the feeling that you are deliberately targeting them. When there is a consolidated changes being introduced it would be viewed as top management commissioned and supported policy.
Get the buy in of the operational HOD's : Ultimately the HOD's would be responsible for their team members adopting the new measures suggested. Getting their buy would make them partners in your plan and you can also get valuable feedback, suggestions and alternate ideas to explore. More importantly they would assist you in effectively implementing the system.
As far as possible highlight the benefit / advantage / usefulness of the change for the employee. This could reorient the thinking from a system being deliberately imposed to a system being reviewed for the betterment of all stake holders. You may have to be creative and stretch your imagination a bit to come up with selling the new system to the employees but it will be well worth your effort.
Listening is the key to cooling off an aggressive person. It is best done along with an other senior person, preferably the employees HOD. Allow them the aggressive person to vent out. Then go about responding using a combination of logical arguments, subtly deconstructing the fallacies or misunderstandings in their concerns and by putting your point across from a perspective not originally visualized by the aggressive employee. Throw in points that make the listener feel less threatened by the changes proposed and possibly show them how the change will actually benefit the employees in the long run.
I can understand your concern as it is really difficult to handle people hiding deep-seated anger. Confronting an aggressive person can be tricky, but you can have open discussion on their issues bothering them.
Firstly, whenever you inform them about new policies or rules, remember to keep their reporting manager in the loop. Conduct meetings to know their point of view. Let them complete their side before you speak.
It is not YOU who is making new policies, make them understand this by showing necessary documents or mails. Do not take it personal and control your anger when you are in a meeting with passive-aggressive employees.
You cannot change the person, therefore it is better to focus on what you can do to improve the situation. Try to be positive throughout your discussion so as to not add to their aggression.
Hope you will deal with them calmly. All the best!
You have got very good inputs from many of our members and I am sure you are considering them.
However I believe that there are always two sides to a coin. It is possible that some changes may be brought with good intention but not executed properly. Secondly make you sure that there is no genuine grievance that is left unheard. The third point is the feedback that has to be going from your side to the policy makers / apex management team. This will ensure that matters do not worsen.