Any open position, including non-base currency, can be closed by IBKR when the account is in a real or projected margin deficit. A Liquidation is done automatically and the Liquidation algorithm decides what to close. Please remember that IBKR's Liquidation system is designed to close positions to reduce margin requirements and ensure the account becomes margin compliant.
If you want to decide what positions to close then you need to actively monitor your account values and add funds or reduce positions when your account's Margin Cushion is low.
You have the ability to request one position be considered to Liquidate Last but that is a request and not a guarantee for what will be closed when the account is in a margin deficit. To choose a specific symbol to "Liquidate Last", while logged into TWS, right click over the desired symbol, and then select "Set Liquidate Last"
Please Note
- IBKR provides customers the opportunity to pre-request the order of liquidation in the event of a margin deficiency in their account, such requests are not binding on IBKR. In the event of a margin deficiency in customer’s IBKR account, IBKR retains the right, in its sole discretion, to determine the assets to be liquidated, the amount of assets liquidated, as well as the order and manner of liquidation. Customers are encouraged to consult the IBKR Customer Agreement and the IBKR Disclosure of Risks of Margin Trading for further information.