An election instruction is the formal response by which an investor tells its intermediary how to act on a corporate action with options. It identifies the account, the security and the event, names the chosen option and gives the quantity of securities to which it applies; a holder may split a position across several options. Some events require extra details, such as a bid price in an auction tender or a certification of the holder's status. The decision itself is described under corporate action election.
Institutions send instructions as structured messages, traditionally the SWIFT MT 565, or through a custodian's portal. The custodian validates the instruction against the client's eligible balance, blocks the securities so they cannot be sold, and passes the election up the chain before the election deadline. Positions without an instruction receive the default option. Whether an instruction can be withdrawn depends on the event terms.