(Bloomberg) -- Directors are stepping down from the boards of five public technology companies after the US Justice Department raised antitrust concerns about individuals advising competing businesses -- the opening salvo in an economy-wide push likely to hit private equity and other financial investment firms.   

The action announced Wednesday marks the DOJ’s first foray in an initiative to enforce a rarely invoked 1914 law against so-called interlocking directorates, where individuals or entities sit on the board of directors for two companies that directly compete with one another.

“The antitrust division is undertaking an extensive review of interlocking directorates across the entire economy and will enforce the law,” Assistant Attorney General for Antitrust Jonathan Kanter said in a statement.

As a result of the DOJ’s action, three directors associated with Chicago private equity firm Thoma Bravo LLC resigned from the board of SolarWinds Corp. SolarWinds confirmed in a public filing on Wednesday that three board members resigned after receiving a letter from the DOJ. The SolarWinds filing noted that the resignations “were not the result of any disagreement with the Company.” 

Thoma Bravo also has an investment in and sits on the board of Dynatrace Inc.

An executive with Netherlands-based private equity firm Prosus NV has also stepped down from the board of online education company Udemy Inc. Prosus also has an investment in and board representation on Skillsoft Corp., according to the Justice Department.

A spokeswoman for Udemy said in a statement that the Prosus representative stepped down due to DOJ’s concerns, but there was “no finding” any law was violated.

Executives have also resigned from the boards of Definitive Healthcare Corp., Redwire Corp. and CTS Corp., according to the Justice Department. Representatives for those companies didn’t respond to a request for comment.

While the law against interlocking directorates has existed for more than 100 years, it has been enforced only sporadically. Last year, two executives from Endeavor Group Holdings Inc. resigned from positions on the board of Live Nation Entertainment Inc. in response to antitrust concerns.

Before that, the last major case took place in 2009 when antitrust concerns led Google’s then CEO Eric Schmidt to step down from the board of Apple Inc. and an Amazon.com Inc. director also stepped down in favor of his position on Google’s board.

Wednesday’s action marks the Justice Department’s first sustained effort to challenge overlapping holdings in decades.

Research has found evidence that competition is diminished when an institutional investor is the largest holder of shares in companies in the same industry. The result can be higher prices and less innovation. One widely cited 2014 paper concluded that airline fares are 3% to 7% higher because of common ownership by big funds.

The Justice Department opened a probe in 2015 into whether the four largest US airlines colluded on pricing during talks with their biggest shareholders, which included BlackRock Inc., State Street Corp., and JPMorgan Chase & Co. among others. The probe closed without any action.

--With assistance from Emily Birnbaum.

(Updates with SolarWinds filing and Udemy comment, beginning in fourth paragraph)

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