Sea-Land Corp. activated its “poison pill” plan.

The plan is aimed at making the international shipper unpalatable to Dallas financier Harold C. Simmons, who wants to acquire it in a hostile takeover. Noting that the Dallas-based Simmons now has more than 35% of Sea-Land’s common stock, company officials decided to trigger an anti-takeover plan approved Dec. 10 by the Sea-Land board of directors. The plan gives current shareholders rights to acquire more stock at a 50% discount, diluting the value of the block held by Simmons.