US mall king Simon Property made a $16 billion hostile offer for Macerich on Monday, after failing for four months to engage the smaller shopping center operator in friendly merger talks.
Simon offered $16 billion, or $91 a share, in cash and stock that represented a 30 percent premium to Macerich's price just before Simon disclosed a 3.6 percent shareholding in November, and about five percent above the company's closing price Friday.
Simon put the total value of the offer at $22.4 billion, when including Macerich's $6.4 billion in debt.
Simon warned the company not to try to block the offer, after having failed several times to convince Macerich's board to negotiate.
"We urge Macerich to forego entrenching defensive tactics that obstruct the will of its shareholders and instead engage in serious discussions with us," said David Simon, Simon Property's chairman and chief executive, in a statement.
"It is our strong preference to work with  Macerich to reach a mutually beneficial agreement, and we are available immediately to meet with Macerich and its advisors."
Macerich confirmed it had received the proposal and would review it.
The deal would combine the country's largest shopping center operator, with about 182 million square feet (17 million square meters) of leasable space in 109 properties, with the mid-sized Macerich, holding 55 million square feet in about 60 properties.
Simon owns the Premium Outlets and Mills chains of suburban malls. It also owns about 30 percent of France's retail property power Klepierre. Macerich's mall  properties are mainly in California, Arizona and the New York region.
Simon said if its bid for Macerich is successful, it would sell some Macerich assets to General Growth Properties.
While making no comment on the offer, Macerich in a statement to shareholders Monday stressed its own success in buying, developing and selling retail properties, and the high value and income of a number of its malls.
The proposed deal comes after a long downturn in the US shopping center industry, only partly tied to the economic crisis of 2008. As US consumer spending picks up slowly, the outlook for some properties is improving.
Macerich shares were up 6.1 percent in midday trade at $91.99, while Simon shares slipped 0.1 percent to $180.42.