Dear Sunita,
In the absence of much information, just going on the content which you have posted, I have certain points to make.
1. Do you allow a grace period? For example, if the office starts at 9:00 a.m., then allowing people to reach the office by 9:10 a.m.
2. Do you have a policy for late arrivals? If not, then it's time for you to create one. For instance, clearly specifying slabs of late arrivals and the resulting consequences.
You could decide on or fix the number of late arrivals permissible, after which it could be adjusted either against salary or paid leaves. For example, allowing an employee to report to duty 15 minutes late twice in a month. Depending on your organization, this time limit could range from 30 minutes to 1 hour. For these late arrivals (though permitted), the employee will have to fill in a late arrival Permission Slip on that very day, get it approved from the immediate Head or Manager, and then submit it to HR for their approval too.
It's a personal experience that such methods do work. There is a very rare possibility that you will have to remind them again. Employees themselves will take care, and even the approving authority will be in the loop.
If the staff size isn't big enough, then please try to find out the possible reasons, followed by counseling. If still nothing changes, then verbal and written warnings should follow. Please make it a point to elaborate on everything step by step very precisely in the policy. This might help you. The most desirable action would be finding the root cause, whether this late coming is just out of habit or if there are other underlying reasons.
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I have corrected the spelling, grammar, and formatting errors in the text.