In a letter to the chief executive officers of the Standard & Poor’s 500 Index, Fink asked the companies to avoid short-term pressures created by the increasing activist shareholder activity of recent years.

“It is critical … to understand that corporate leaders’ duty of care and loyalty is not to every investor or trader who owns their companies’ shares at any moment in time, but to the company and its long term owners,” Fink wrote in the letter, dated March 31.

BlackRock (BLK) is the world’s largest asset manager. At the end of 2014, it had $4.65 trillion of assets under management.

In 2014, dividends and buybacks in the United States totaled $900 billion, the highest ever, according to the letter. Through March, buyback authorizations totaled $257 billion, the fastest start to any year on record, according to Birinyi Associates.

Many market analysts expect that a rise in interest rates will not derail the buyback boom bolstering stocks.

The company made Fink’s letter available to Reuters after The New York Times first reported on the document on Monday evening, ahead of the company’s scheduled release of first-quarter results on Thursday.

Given the low interest rate environment, such moves “send a discouraging message about a company’s ability to use its resources wisely and develop a coherent plan to create value over the long-term,” Fink wrote

Corporate boards should act as “the first line of defense” against short-term pressures.”

In the last two years, activists have taken positions in some of the largest U.S. corporations seeking larger share repurchases, divestitures or other corporate action. The companies targeted included Apple Inc, General Motors Co, DuPont and Qualcomm Inc.

Hank Smith, chief investment officer of Haverford Trust, which has $8.2 billion in assets under management, disagrees with Fink and believes most activists now are more long-term than the corporate raiders of the 1980s.

“I think the majority of activist investors today are really investors and are not going into this to slash and burn,” Smith told Reuters in an interview Tuesday afternoon.

For example, Smith applauded Nelson Peltz’ Trian Fund Management for taking a long-term approach with its campaign against the management of chemicals and agricultural company DuPont (DD).

Trian is pushing the company’s board to be more accountable and argues it should be split in two. The fund is pushing for four seats on DuPont’s board.

“I think Trian represents a positive influence,” he said.

Smith also disagrees with Fink that dividends are a sign companies are thinking short-term.

“Dividends are the mother’s milk of returns to investors,” said Smith, who only invests in companies that pay them. “Dividend increases are the most tangible statement management can make about the firm’s fundamentals and future prospects.”

For its part, BlackRock has revised its proxy guidelines to highlight it expects board members to protect shareholders against short-term thinking.

Firms that have a long-term strategy to create shareholder value, as well as credible metrics to assess performance, will have BlackRock’s support during periods of underperformance.

“In such cases, we will take action to ensure that the owners’ interest are effectively served,” he wrote.

Dan Fuss, vice chairman of Loomis Sayles and known as the Warren Buffett of bonds, shared Fink’s sentiments.

“In a number of cases, in the tech area among the most prominent of the examples, is where you ought to be reinvesting in the business,” he said. “There’s too much catering to quarterly earnings engineering slash activist shareholders.”