WASHINGTON (CN) – A campaign watchdog group is pressing the Federal Election Commission to investigate how the National Rifle Association spent money in relation to four past senatorial campaigns.

In a complaint filed with the FEC Monday morning, the Campaign Legal Center alleged the NRA used a shell company to funnel money into campaign ads while another straw company took in money and acted as a “common vendor” for the four campaigns.

The Center claims the scheme involved two separate NRA entities: the National Rifle Association of America Political Victory Fund and the National Rifle Association of America Institute for Legislative.

According to the complaint, these entities contracted with the consulting firm OnMessage, Inc. during the 2010 and 2012 election cycles, and then, in 2013, OnMessage formed another consulting company, Starboard Strategic Inc.

During the next election cycle, the complaint says, both NRA entities worked with Starboard Strategic Inc. to support three senatorial candidates, Thom Tillis, R-N.C., Tom Cotton, R. Ark., and Cory Gardner, R-Colo. Meanwhile, the Center says, all three candidates’ campaign committees were paying for the services of OnMessage.

In 2016, Sen. Ron Johnson, R-Wis, received similar support from the NRA organizations through one company while paying another, the complaint says.

The complaint alleges that the two companies, which share a business address, are “indistinguishable” from another. It also points to several awards won by OnMessage for campaign ads that Starboard was contracted to make. The Center claims it even found language on both companies’ creative websites were virtually identical.

“OnMessage created Starboard for the purpose of disguising the [NRA orgs’] coordinated communications,” the complaint says. “As a result, the [NRA orgs] made excessive and unreported contributions to those campaign committees, in violation of FECA’s reporting requirements and contribution limits.”

The Center claims the scheme is ongoing with $3.5 million in spending from the NRA orgs to Starboard during the 2018 election cycle.

“There is substantial evidence that the NRA funneled millions through a shell corporation to unlawfully coordinate with candidates it was backing,” said Brendan Fischer, director of the Campaign Legal Center’s Federal Reform project.

“According to the Supreme Court, groups like the NRA can only make unlimited expenditures if they are independent of the candidates they support, and it falls to the FEC to enforce the laws that preserve that independence and prevent corruption,” he said.

The complaint asks the FEC to open an investigation into the campaign spending and for “appropriate sanctions” for any and all violations the investigation finds.

Attempts to reach Senators Tillis, Cotton, Johnson and Gardner, and the NRA organizations were unsuccessful.