School of Management and Yale Law professor Ian Ayres is threatening to publish a study that will unveil the full — and arguably excessive — costs of many American corporations’ retirement savings plans.

Ayres has sent letters to roughly 6,000 employers warning them that he will publish the results of his study on Twitter and tag each company separately, as well as make the results available to major newspapers, including The New York Times and The Wall Street Journal. In his study, Ayres examined 401(k) plans — employer-sponsored plans that allow participants to save and invest for retirement — to highlight the high fees associated with many of them.

One of the letters reviewed by WSJ said Ayres and his research partner used data from filings made to the Department of Labor in 2009. Critics of the study have questioned the legitimacy of the 5-year-old data, claiming that many 401(k) plans now disclose more complete information about their fees.

Ayres has said he and his research partner, Quinn Curtis, associate professor at the University of Virginia School of Law, plan to publish the results of their study in spring 2014.