David Brock, shown in this 2010 file photo, has resigned from a super PAC that’s poised to support Hillary Clinton in a potential White House campaign. (Katherine Frey/The Washington Post)

A clash over fundraising tactics between operatives running a network of super PACs poised to back a Hillary Rodham Clinton presidential run led liberal activist David Brock to angrily break ties Monday with one of the biggest groups in the coalition.

Brock — who runs a suite of groups already churning out research to boost Clinton and impale her potential GOP rivals — stepped down from the board of Priorities USA Action after a story in the New York Times raised questions about a donor consultant who works with his organizations.

In a sharply worded letter, Brock accused current and former Priorities officials of fueling a “specious and malicious attack” against American Bridge and Media Matter by providing information for the piece, which he called “an orchestrated political hit job,” according to a copy obtained by The Washington Post. Brock’s departure was first reported by Politico.

Brock’s sudden, heated resignation exposes a deep tension among the coterie of Democratic strategists jockeying to play a role in the upcoming White House contest, a race in which independent groups are expected to have more prominence that ever.

The Priorities board was carefully built to bring together major players from across the party, and Brock’s departure raises questions about whether the break will impede coordination among the pro-Clinton groups.

Priorities, which began as a super PAC to support President Obama’s reelection, is mobilizing to be the main outside-advertising vehicle supporting Clinton, while Brock’s American Bridge was expected to provide research for Priorities and other independent groups.

Neither Brock nor Priorities officials immediately responded to requests for comment.

One person familiar with the situation said that the dispute centers largely on a debate about how donors on the left should be solicited and a perception that Bridge officials had sought at one time to funnel contributions through their organization.

“There are a lot of deep relationships here and issues as to how donors are approached,” said the person, who declined to be named to describe private discussions. “I think they will figure it out because there is all-around a strong set of connections with fundraisers. I don’t think this will have broader consequences.”

In his letter, which was addressed to Priorities co-chairs Jim Messina and Jennifer Granholm, the former governor of Michigan, Brock said he was told by multiple people that Priorities officials fed information to the Times for its piece. The story described the lucrative commissions earned by Mary Pat Bonner, a donor adviser who works closely with Brock’s organizations, as well as another group, Ready for Hillary.

“This disheartening conduct and serious breach of trust between organizations that are supposed to work together toward common ends has created an untenable situation that leaves me no choice but to resign my position,” Brock wrote. “The apparent purpose was damaging our fundraising efforts, while presumably enhancing Priorities’ own.”

Brock wrote: “Frankly, this is the kind of dirty trick I’ve witnessed in the right-wing and would not tolerate then. Our Democratic Presidential nominee deserves better than people who would risk the next election -- and our country’s future -- for their own personal agendas. Despite this unfortunate incident, American Bridge’s donor base is secure and we remain undeterred in our plans to execute strategies to win the next election.”