WASHINGTON (CNN) Three watchdog groups on Tuesday urged federal campaign regulators to pursue civil penalties against President Donald Trump's campaign, saying special counsel Robert Mueller's team had created a "roadmap" for action.

Mueller's team did not charge Donald Trump Jr. and other campaign aides with breaking any laws by participating in a June 2016 meeting with a Russian lawyer at Trump Tower. Trump Jr., Jared Kushner and then-campaign chairman Paul Manafort met with Russian lawyer Natalia Veselnitskaya after an email exchange between Trump Jr. and a publicist about potential dirt on Hillary Clinton.

The Campaign Legal Center, Common Cause and Democracy 21 on Tuesday filed a supplement to an earlier complaint the groups filed in July 2017, asking the Federal Election Commission to investigate the meeting for a possible violation of campaign finance law. Civil penalties under that law, they said, did not require regulators to prove "willful" violations.

"There is no 'willful' requirement for civil enforcement by the FEC, which need only find reason to believe that Trump Jr. solicited a contribution from a person he knew was a foreign national," Brendan Fischer of the Campaign Legal Center said in a statement.

The Mueller report provides a "roadmap" for the federal election regulators to follow, the groups said.

FEC officials declined to comment Tuesday, citing agency rules against discussing specific matters pending before the agency.

The Trump campaign had a familiar refrain when asked about the watchdog groups' efforts.

"The witch hunt continues," Trump campaign spokesman Tim Murtaugh said.

Last week, FEC Chairwoman Ellen Weintraub said the Mueller report raised issues that fall "squarely" within the agency's purview and asked the commission's lawyers to look at the report to determine whether its findings contain information relevant to ongoing enforcement matters.

Despite Weintraub's interest, it's far from clear that the agency will take any action. The commission often deadlocks along partisan lines on enforcement issues.

Donald Trump Jr.'s lawyer, Alan Futerfas, did not immediately respond to a request for comment Tuesday about the updated FEC complaint.

In a statement earlier this month, Futerfas said the Mueller report vindicated the President's oldest son.

"The report confirms that the June 9, 2016, meeting was just what Don said it was, and nothing more, and that there was nothing improper about potentially listening to information," he said.

The complaint from the watchdog groups centers on the meeting at Trump Tower in New York between Veselnitskaya and senior campaign officials.

Tweets published by Trump Jr. in 2017 include an email that publicist Rob Goldstone sent to him on behalf of client Emin Agalarov to suggest a 2016 meeting regarding potential dirt on Clinton during the presidential campaign.

"This is obviously very high level and sensitive information but is part of Russia and its government's support for Mr. Trump," Goldstone, who represented Agalarov, the son of an Azerbaijani-Russian businessman close to Russian government, wrote in the email to Trump Jr.

"If it's what you say I love it," Trump Jr. replied, according to an email he released.

The damaging information on Clinton never materialized, the President's son later said in Capitol Hill testimony . And Mueller's team decided against bringing a campaign-finance criminal case.

"Taking into account the high burden to establish a culpable mental state in a campaign-finance prosecution and the difficulty in establishing the required valuation, the office decided not to pursue criminal campaign-finance charges against Trump Jr. or other campaign officials for the events culminating in the June 9 meeting," Mueller's prosecutors said in their report.