My experience is you need to attach your pay stub past 6 month to show your employed status. You also need to add your financial status shown by letter from your bank on your saving, check, stock, house assset, morgage etc, as well as your W-2, 1099 and Federal tax return report past three years if they are available. Of couse, it is not bad to have an employment letter for your employer. All of those are for avoiding potential RFE. Just for your reference and all of these are required by my attorney.