First and foremost, I apologize for taking so long to answer your question. I was out sick last week and I’m just answering my mail now.
As for the appeals process, progressive discipline policies and procedures, including appeals, are typically the subject of specific negotiation between the company and employer. I’m assuming that in this case, the employees are non-union and that you can pretty much establish terms unilaterally. But even in non-union workplaces, you need to be aware and try to adhere as closely as possible to your previous policies, especially if the changes you want to impose are unfavourable to employees.
The actual appeal procedure should basically:
i. indicate which determinations can be appealed–typically, appeal rights should cover only more serious forms of discipline like suspensions and termination–unless you want to go down the road of having different appeals processes and timelines for different kinds of offences;
ii. explain what an employee must do to appeal, which can be as simple as writing a letter to HR stating the employee’s decision to appeal and the reasons he/she thinks the action is unfair; and
iii. list a timeline for an appeal, like within 5 to 10 days of the date of the disciplinary action.
You should probably also say something about who will decide on the appeal, within which timeframe and on the basis of which criteria. In collective agreements, there’s typically a fairly elaborate provision outlining the procedural rules of a proceeding, like how each side can make their presentations, etc.
Of course, you also need to be sensitive to the needs of your own organization and situation, like whether it’s subject to a regulatory authority or a corporate parent, etc.  Hope that helps and sorry again for the long delay. Glenn