Macy’s planned closure of 150 locations could spell trouble for mall landlords on the hook for billions of dollars in debt.

The retailer anchors at least 80 malls behind approximately $24B in commercial mortgage-backed securities, according to data from CoStar Group and Morningstar DBRS.

About $3.6B of that debt is already in special servicing, meaning the malls are having trouble repaying the loans, and the majority of that is tied to three of the country's biggest mall owners: Brookfield, Simon Property Group and Unibail-Rodamco-Westfield, according to CoStar.

Macy's CEO Tony Spring said on the company's earnings call last week that the department store chain is looking at the markets in which it operates “with a focus on being in the strongest centers.”

The New York-based company hasn't disclosed which stores it would look to shutter, but if it goes through with the plan, it would reduce its already-diminished store count by 30%, leaving it with 350 locations.

The company could look to sell those boxes. Spring said on the call that selling closed stores and distribution centers would generate between $600M and $750M.

Macy’s stores going dark could diminish revenue for landlords as foot traffic falls. In malls where the retailer is an anchor, closures could trigger other stores to pull out or alter their rent agreements with property owners due to co-tenancy clauses, CoStar reported.

The company's plans carry an air of uncertainty. Although Macy’s rejected a bid from activist investors Arkhouse Management and Brigade Capital Management to go private, the firms countered this week with a $6.6B cash offer.