NEW YORK CITY—Asserting that the retailer's property assets are worth $21 billion by themselves, activist investor Starboard Value LP is pressuring Macy's Inc. to split its real estate into two or more joint ventures. A Starboard presentation made public on Monday cites the success of recent JVs between Hudson's Bay Co., owner of Saks Fifth Avenue, and shopping center REITs Simon Property Group and RioCan Real Estate Investment Trust.

Starboard, which disclosed a stake in Macy's this past July, has repeatedly called on the Cincinnati-based retailer to monetize its real estate. Its most recent call to action comes a few days after Macy's reported disappointing same-store holiday sales and said it had hired Eastdil Secured to help market stakes in its owned stores.

Among those stores is the iconic flagship location in Manhattan's Herald Square. Starboard estimates the property's value is nearly $4 billion, or nearly half the combined value of the retailer's 407 owned mall locations, according to the Starboard presentation. The investor's proposal suggests one JV for flagship properties such as the Herald Square store and another for mall locations.