NEW YORK (AP) — Chipotle, which is trying to revive its fortunes after being rattled by food safety scares, says a third of its board members will leave in May after their terms expire.

The burrito chain, under pressure from activist investor Bill Ackman to speed up its recovery, expanded its board to 12 members in December after four new directors, approved by Ackman, were added. Ackman’s hedge fund, Pershing Square Capital, is one of Chipotle’s largest shareholders, owning a more than 10 percent stake in the chain.

In a filing Friday, Chipotle said the four members who won’t seek re-election in May are John Charlesworth, Patrick Flynn, Darlene Friedman and Stephen Gillett.

“These departures are the product of individual decisions, and are in no way part of our agreement with Pershing Capital and Mr. Ackman,” said Chipotle spokesman Chris Arnold.

Chipotle Mexican Grill Inc., based in Denver, is trying to win back diners after a 2015 E. Coli outbreak sickened some customers. Sales fell 20 percent last year at its established locations, even as it gave away millions of free burritos, launched a temporary loyalty program and worked on improving its customer service.