1. I hope that there is a very clear attendance policy in place.
2. I would hope that there is a solid attendance tracking utilized.
Even if there is an existing policy, a re-visiting and re-signing may be worthwhile with formal communication with the employee pool.
Make sure the employees understand what is required and why it's required. Help paint the picture of what the impact of absence/tardiness is on their own work experience/performance as well as that of others.
Your GM should also understand that lack of holding people accountable for one key expectation increases the difficulty of upholding other expectations and has a ripple effect on employee (and hence company) performance.
You may want to consider even enforcing it retroactively depending on how your company policy is written. If not, define a very specific time in which it WILL be enforced and do so. Clearly define any exceptions to the policy and adhere to those guidelines.
On the flip side, celebrate the positive. Acknowledge those that do adhere to the policy. Also, illustrate and communicate the positive impact that the return to broad policy-adherence has on the individual and company performance.