At issue in Bevin's first ad is the lack of a written on-screen disclaimer. Political advertising is required by campaign law to include text at the end identifying the candidate and stating that he or she approves the ad.
Bevin's ad includes only text reading "Paid for by Matt Bevin for Senate, Inc." and lacks text declaring the candidate approves the message.
In a letter to Kentucky television station WAVE, McConnell's campaign counsel Sean Cairncross and Chris Winkelman outlined the violation and called for the station to stop airing it.
"As counsel to McConnell Senate Committee ‘14, we write to inform you that Matt Bevin’s authorized campaign committee, Matt Bevin for U.S. Senate, is running an advertisement on your station that contains inadequate disclaimers in violation of federal law. As a result of the violation described more fully below, we urge your station to immediately cease airing Mr. Bevin’s advertisement," they wrote.
A representative from the station said the campaign is revising the ad to comply with federal laws.
Bevin's campaign did not immediately respond to a request for comment.
While the issue is a relatively easy fix, the letter from the McConnell campaign is an early indication the incumbent plans to lean heavily on Bevin in the primary race.
McConnell's campaign launched an ad attacking his opponent as "Bailout Bevin," because of a grant he obtained to help his company rebuild after a fire, on the first day of the primary fight.
And aides for both candidates traded barbs in the news for days prior to Bevin's official announcement.
The already heated back and forth reflects in part the facts that McConnell is facing low approval in Kentucky and he's long been vulnerable to a Tea Party challenge.
Conservatives believe the Senate minority leader has been too liberal during his time in Congress, citing his votes for the financial bailout and debt-ceiling increases, among others.
And on Wednesday, a number of conservative groups that typically back challenges to incumbents signaled an openness to supporting Bevin.
But McConnell remains the heavy favorite in the race. He's amassed nearly $10 million in campaign cash and is building a presidential-level campaign operation for his reelection fight.
Read the letter:
--This piece was updated to reflect comment from the station.