Options:
1. Change the combobox RowSource as suggested and return to the parameterized query with LIKE operator. Oops, not working because the field is number type. Make EmpBadgeNum field a text type and LIKE operator can be used. Probably should be text because it is identifier data, not really a number value that would be used in math calculations like Price * Quantity.
2. Conditional code to set the WHERE CONDITION, something like:
DoCmd.OpenReport "Operator's ID Card", acViewPreview, , IIf(IsNull(Me.Emp), "", "EmpBadgeNum=" & Me.Emp)
or if the field were text type:
DoCmd.OpenReport "Operator's ID Card", acViewPreview, , "EmpBadgeNum LIKE '" & Me.Emp & "*'"
If you do change the field type of EmpBadgeNum primary key will have to also change the field type of the related foreign key fields.