Because top fund managers like BlackRock rarely discuss their votes in detail, filings in late August to the U.S. Securities and Exchange Commission provide a rare window into the influential ballots they cast at springtime shareholder meetings like the one held by Exxon on May 25, one of this year’s more contentious.

BlackRock, which manages nearly $5 trillion, has been criticized for largely supporting company managers on matters like executive pay or electing directors. BlackRock funds have backed corporate directors around 97% of the time since 2013, according to research firm Proxy Insight, and mostly backed Exxon at this year’s meeting such as opposing shareholder proposals addressing climate change.

BlackRock executives say they prefer to press companies behind the scenes, and vote against management only when such engagement fails. But in a rare break, filings on Friday showed funds including the $45 billion BlackRock Global Allocation Fund withheld support from Exxon directors Jay Fishman and Kenneth Frazier this year.

Fishman, who recently passed away, had been CEO of insurer Travelers. Frazier is CEO of drugmaker Merck (MRK).

While spokesman for BlackRock and Exxon declined to comment, BlackRock’s reasoning for the votes appears to be spelled out in a recent governance report on its website. The report describes how BlackRock executives tried to discuss strategy and capital allocation with independent directors of an unnamed “large oil and gas corporation,” but were rebuffed because of a policy against such talks.

As a result, BlackRock said it withheld support from the company’s lead independent director and the chair of the committee that set the policy. Fishman had been Exxon’s “presiding director,” meant to provide independent board leadership according to Exxon’s proxy statement, while Frazier led its board affairs committee.

The two were re-elected with 88% and 90% of votes cast, respectively, down from 95% and 98% in 2015. BlackRock is Exxon’s second-largest shareholder with about 6% of its stock, according to the proxy. Exxon’s other directors got no less than 95% support this year.

How much contact independent directors should have with outsiders has become a loaded issue because of the rise of activist investors pushing disruptive agendas.

Asked about BlackRock’s concern, Exxon spokesman Alan Jeffers cited a webpage outlining board communications procedures, which do not directly address the matter. But Tim Smith, who leads shareholder engagement efforts at Walden Asset Management, said Exxon executives have described at meetings the sort of policy criticized by BlackRock.

Filings also showed BlackRock funds did not back resolutions at 3M (MMM), Illinois Tool Works (ITW) or Xerox (XRX) calling on the companies to exclude the impact of share buybacks when calculating executive pay, even though the resolutions cited the concerns about buybacks raised by BlackRock CEO Larry Fink.