Here is how disciplinary action works against an hourly employee. This should clear up any confusion you have because it simply does not make sense to file a grievance against disciplinary action on your attendance because we have records that will in fact show if you suck at showing up to your job. I see that you are a 22.3...
There are two categories of discipline. Each of these are separate from one another meaning that the levels of discipline cannot advance from one category to another:
Attendance:
Enough Said. Come to work, and be on time!
Service and Everything else:
You can be disciplined in progressive steps for service and other disorderly like conduct such as cursing at management, throwing packages or hand scanners, stealing time, low PPH, ect...
Now you are probably wondering how an employee can be punished for PPH when the contract clearly states, "A fair days work for a fair days pay." You could even make the argument from a shop stewards perspective, and say that everyone is different and therefore has different capabilities. Fine. However, if I look on GSS for a loader's PPH or do a flow count on a sorter I will either work with the employee to improve it, or if it is acceptable I will then review the employee's performance with them and then tell them that they have now sat their own MAR. I can now hold them accountable to that performance. I have seen what they are capable of, and expect to it to maintain.
The appropriate levels of discipline include: warning letter, five day suspension, ten day suspension, last chance agreement, and finally termination. A talk with is just a courtesy and is not a requirement. However, most reasonable management people will do a talk with. This is only fair because how can an employee correct a problem if they do not know there is one? Communication is key, and I can only hope that you have a management team bright enough to know this.