Three of the new companies landing on this year’s list are newcomers to the Fortune 500, and three previously had a female board member who has since retired, transferred, or left the company.

“One can certainly understand there could be extenuating circumstances for some companies, but for those who have been in the spotlight by being in the Fortune 500 list before, they certainly should have responded to the enormous amount of public concern about women’s equality and getting women on corporate boards,” said Heidi Hartmann, the president of the Washington-based Institute for Women’s Policy Research think tank . “I would have expected them to have responded.”