Dear friend,
If there is less punctuality in your office then it can be said it has part of the culture of your company. Changing culture is always difficult. As a first step, you may issue the circular and express your concern about lack of timeliness. At the same time, start monitoring the records of the attendance. Those who are habitual offenders, call them and have a one-on-one session. Explain the importance of maintaining a culture of discipline. You will find that few are still intractable. For them, for every three late comings, deduct their half day salary. Even after deduction of salary also, you will find few are still stubborn. For them continue with the salary deduction and after deduction of salary for 2-3 times, issue show cause notice for why stern action will not be taken against them. Terminate 1-2 persons and then it will send a right signal to one and all.
By the way, what is your designation? Before taking action, take leadership into confidence. If leadership itself is lenient on office discipline then better to allow to go on the things as they are!
About Casual Leave: - Assigning reason for "casual" leave may not be mandatory. Casual leave is granted so that employee can meet unforeseen and immediate requirements. Secondly, as long as an employee avails of a casual leave within authorised number of days, then it should not be a problem.
Thanks,
Dinesh Divekar