Alcoa said it adopted an anti-takeover plan.

Aluminum Co. of America said it will seek shareholder approval at its annual meeting May 10 of two measures aimed at discouraging acquisitions of its stock: One would prevent so-called greenmail by forbidding the company from paying a premium to repurchase shares from holders of 5% or more of the voting stock without approval by a majority of shareholders. The other would stagger directors’ terms--a third being elected each year--to discourage a third party from effecting “an unreasonable, sudden or surprise change in the composition of the board without the support of incumbent directors.”