What, I would suggest is to draft a common email mentioning the issue (don't point out anyone but keep it a general) and intimate them if the rule is not followed properly then strict action will be taken.
If the situation not improved send reminder for the same on fortnight or weekly basis. And finally at the end of the month you may take action by deducting salaries, issuing coc etc.
Also, if you are not using any HR or payroll software then go for it as it will help in managing employees very well in an easy way.. You can try SaralPayroll that comes with employee management as well as attendance management module that will help in monitoring employee attendance etc. Initially you can try its free or trial version.
8th November 2013 From India, Lucknow