Washington (CNN) A gun-safety group is suing the Federal Election Commission for failing to act on its complaints claiming a pattern of the National Rifle Association improperly coordinating its political spending with Donald Trump and other Republican candidates in recent elections.

The lawsuit , while focused on forcing the Federal Election Commission's hand on a technical timing issue, seeks to put a spotlight on a broader question: the NRA's role in recent elections and whether the powerful gun lobby skirted contribution limits to provide an unfair advantage to Trump and other candidates it backed. The NRA denies any wrongdoing.

Giffords, a gun-control group run by former Arizona congresswoman and gun-violence survivor Gabby Giffords, and the nonpartisan Campaign Legal Center Action contend in the suit that the FEC has missed a 120-day deadline to act on four complaints brought by the groups.

The lawsuit, provided first to CNN, asks a federal judge to intervene and prod the agency to move ahead with investigations.

The court filing precedes Trump's address Friday to the NRA's annual convention in Indianapolis.

Improper coordination?

A political action committee cannot donate more than $5,000 to a candidate in a single year and an individual was barred in 2016 from giving more than $2,700 to a candidate for the primary or general election. But federal law allows individuals, corporations and unions to spend any amount with outside groups, such as the NRA's political arm, to influence candidate elections -- provided they do not coordinate their spending operations with the candidates they support.

The lawsuit and underlying complaints allege that as much as $35 million that the NRA spent to support several GOP candidates over three election cycles amounted to illegal donations because the NRA's ads were placed by consulting firms that also were handling ads for Republican candidates supported by the powerful gun-rights lobby.

The NRA engaged in a "complicated scheme to coordinate its spending" with candidates "while taking steps to conceal its coordination," the lawsuit, filed in federal district court in Washington, alleges.

"We scrupulously follow the law," NRA spokeswoman Jennifer Baker said in a statement to CNN. "This latest effort by Giffords and the Campaign Legal Center is a frivolous lawsuit based on a frivolous complaint."

Federal Election Commission officials declined comment, saying it is against agency policy to comment on pending litigation. The Trump campaign also declined to comment.

The NRA spent more than any other independent outside group to back Trump's campaign, pumping in more than $30 million to boost him and attack his Democratic rival, Hillary Clinton, in 2016, according to a tally by the nonpartisan Center for Responsive Politics.

But its spending on Trump's behalf has faced intense scrutiny.

The disclosures that television stations file with the Federal Communications Commission show that four individuals who placed pro-Trump ads for the NRA's political arm also placed ads for Trump's presidential campaign, the lawsuit said.

The individuals worked for either Red Eagle Media, which placed NRA-related ads, or American Media & Advocacy Group, which handled the Trump campaign's ads. Both firms share an Alexandria, Virginia, address and are affiliated with a third company, National Media Research, Planning and Placement, according to the lawsuit.

Trevor Potter, a former Republican chairman of the Federal Election Commission and the Campaign Legal Center's president, said that if the NRA's media buyers coordinated their strategy with candidates' campaigns, that would amount to excessive in-kind campaign contributions. The legal center is working as a counsel in the case, alongside Giffords' lawyers.

It's not unheard-of for a single vendor to handle the advertising for both an outside group and a candidate. But to avoid running afoul of federal regulations, companies erect "firewalls" to prevent information flowing between a candidate and the outside group.

Officials with the parent company National Media declined to comment on the record about the complaints and lawsuit.

The FEC will have to determine whether having the same people sign media-buying forms for the candidates and the NRA amounted to a breach of the firewall, experts say.

Signing a media-buying form can represent a "ministerial task rather than a strategic function," said Charlie Spies, a veteran Republican campaign-finance lawyer in Washington. "Having the same person on the forms is an optics issue, but not necessarily a legal issue."

The lawsuit and complaints cite reporting from several media outlets -- including Mother Jones and The Trace , a digital news operation that receives some of its funding from gun-control groups.

The scrutiny about the alleged violation of coordination rules has extended to Capitol Hill, where two Democrats, Sen. Sheldon Whitehouse of Rhode Island and Rep. Jamie Raskin of Maryland, penned a letter earlier this year to the NRA, demanding more information about the arrangement.

Deadlocked agency

Initiating an FEC investigation -- or any significant action at the agency -- requires four FEC commissioners to vote to approve the move. The six-member body has two vacancies, and the remaining commissioners often can't agree on enforcement actions.

Partisan gridlock has been building for years and resulted in the agency deadlocking on nearly a third of its major cases in 2016 -- up significantly from a decade earlier, according to an analysis by a former FEC chairwoman, Ann Ravel. At the end of 2018, the agency had 329 pending cases, including several related to possible violations that occurred during the 2016 election, according to Ellen Weintraub, the commission's current chairwoman. That's up from 100 open cases in 2010, she said.

Increasingly, groups focused on greater regulation of money in elections are pursuing action in court to force the agency's hand. By filing a lawsuit over the delay, Giffords and the Campaign Legal Center want a federal judge to demand that the FEC explain how it is handling the investigation, if at all, and provide regular updates.

Weintraub, a Democrat, has expressed dismay with the gridlock and announced plans earlier this year to take a dramatic step: She won't allow the FEC's lawyers to defend the agency when it is sued for not enforcing the law.

Given the four-vote requirement for agency action, her no "vote" serves as a veto on any effort to initiate a legal defense.

In an interview with CNN, Weintraub said she could not comment on the lawsuit focused on the NRA but that she is not necessarily opposed to extending her refusal to defend the agency to cases involving lengthy delays in agency action.