Jennifer Baker, a spokeswoman for the N.R.A.’s lobbying arm, said Mr. Cox and Mr. LaPierre had “worked closely together for a quarter of a century, and any notion that Chris participated in a coup is absurd. Chris Cox is known as a calming force who always acts in the best interests of our members by effectively defending the Second Amendment, so it’s not surprising that board members would reach out to him for advice during tumultuous times.”

But Carolyn D. Meadows, who succeeded Mr. North as N.R.A. president, said in a statement: “I fully support the actions undertaken today. The N.R.A. is moving forward on all fronts, especially with regard to serving our members and focusing on the crucial upcoming elections.”

The genesis of the dispute between the N.R.A. and Mr. North is a related legal battle between the N.R.A. and its most prominent contractor, the Oklahoma-based advertising firm Ackerman McQueen, which employed Mr. North. The N.R.A. has sued Ackerman, claiming it withheld documents and records from the gun group, and some officials have suggested the company may also have been overbilling. Ackerman, which has said it did nothing improper, filed a countersuit claiming that it was smeared by the N.R.A.

In yet another lawsuit, the N.R.A. has accused Ackerman of breaching confidentiality clauses in its contract and smearing Mr. LaPierre.

The new lawsuit seeks to block Mr. North’s attempt to have the N.R.A. pay his legal fees, which he has sought as he fields requests to cooperate with other litigation as well as a Senate inquiry.

“The N.R.A. believes that Col. North seeks payments from the Association to which he is not entitled,” the N.R.A.’s outside counsel, William A. Brewer III, said in a statement. (Mr. North is a retired Marine lieutenant colonel who first came to prominence during the Iran-Contra hearings.) “The N.R.A. alleges that Col. North breached his fiduciary obligations — in a coordinated attack against the N.R.A. and Wayne LaPierre that involved others motivated by their own economic self-interest,” Mr. Brewer added.

In addition to implicating Mr. Cox, the new lawsuit claims that another N.R.A. board member, the former Oklahoma congressman Dan Boren, participated in the effort to oust Mr. LaPierre, and it presents a piece of evidence intended to shed light on the overbilling question.