Billionaire activist investor Carl Icahn reportedly is placing a $400 million bet against struggling malls, taking on two of the largest investment firms

His trades have pitted him against Putnam Investments and AllianceBernstein Holding LP, two of the largest money managers, the Wall Street Journal said.

Icahn has placed his bet on if mall owners will run into challenges servicing their debt and suffered early losses, sources toldWSJ.com.

Traders in market told the Journal that Icahn “likely is the largest short-seller of mall debt.”

Dan McNamara, a principal at MP Securitized Credit Partners, a New York hedge fund, told the Journal it was “the biggest battle in the mortgage bond market today.”

Top malls remain a draw for shoppers and are receiving interest from institutional investors at a time when weaker properties have struggled, hurt by the rise of e-commerce and store closures.

Icahn isn't the only investor with an optimistic eye on malls.

Brookfield Property Partners LP has boosted its bet on malls, adding exposure to a corner of the real estate market that some of the firm’s investment rivals are avoiding, Bloomberg said.

Brookfield recently bought JPMorgan Chase & Co.’s holdings in four U.S. shopping centers in which the firms were co-invested, said people familiar with the matter. New York State Teachers’ Retirement System also had a stake in two of the malls, one of the people said. In a simultaneous deal, JPMorgan and NYSTRS bought Brookfield’s stake in a fifth mall, the Bridgewater Commons in New Jersey.

The transaction valued the five malls at $3.2 billion, including debt, said the people, who asked not to be identified because the transaction is private.

Representatives for Brookfield, JPMorgan and NYSTRS declined to comment.

Icahn also remains active on other investment news and seemingly always in the headliens.

Icahn on Monday urged the U.S. Securities Exchange Commission (SEC) to rethink a proposed rule change for proxy adviser firms, saying it would make activist investing "even more difficult and expensive to practice."

The SEC earlier this month put forward new rules that would require proxy adviser firms to give companies a chance to review proxy materials before they are sent to shareholders, Reuters said.

"I believe the current proposal - which would subject proxy advisory firms to onerous regulations - is a dangerous misstep that will have disastrous repercussions for the U.S. economy," Icahn wrote in an opinion piece for The Wall Street Journal.

"This odd arrangement would allow corporations to interfere with advisers' research - a recipe for disaster," Icahn wrote, asking the regulator to "rethink" the proposal.

Proxy advisory firms tell investors how to vote on governance issues in corporate elections and cast ballots on behalf of some asset managers. The role of proxy advisers has gained more attention in recent years as the firms have become more influential.