PSA said it has adopted an anti-takeover plan.

Hoping to ensure that PSA Inc. shareholders receive “fair and equal treatment” in the event of a takeover attempt, the San Diego-based airline holding company’s board of directors announced the distribution of purchase rights for a new series of preferred stock. The rights, which would be exercisable only if another company or group acquires 20% of PSA Inc.’s common stock, would not prevent a takeover but would encourage any would-be suitor to negotiate with PSA’s board, according to Chairman J. P. Guerin.