In most contracts you are allowed to be 'skipped over' until either the last most junior person is called back or X period of time elapses, or both. If you defer your recall, they'll call the next person down the list... then the next time they need to recall pilots the ones who deferred the last time are called first again, since they'd be the most senior and they have the option of accepting then or deferring again, rinse & repeat until all pilots are recalled.
If they recall the most junior pilot then usually all the pilots who deferred are required to come back or resign.