1. Go to the General Ledger home page.
2. In the lower left section, "Other", select Fiscal Period Definitions:
3. In the query that pops up, select the fiscal years you want to see and then click the green Run Query button top right.
4. Check the "Posting Prohibited" checkbox on the desired periods and then click the green Update Records button top right. (You can also query the periods you wish to restrict and then use the Batch Update capability to update multiple checkboxes at once.)
(Reverse the process to allow posting in fiscal periods where the year has not yet been hard closed.)