AUGUSTA, Maine — The Maine Ethics Commission handed down the largest fine in the agency’s history Thursday against an out-of-state political action committee that spent nearly $400,000 on attack ads against five Democratic lawmakers last October.

Commission members voted unanimously to fine the Republican State Leadership Committee $26,000 for failing to file timely and accurate reports about the expenditures. The panel originally had recommended a $41,000 penalty but agreed to a smaller fine after considering legal arguments from the PAC.

Ultimately, the commission determined that the late filings delayed $160,000 in matching payments through Maine’s public campaign financing program to the targeted Democrats, all of whom lost their campaigns to GOP opponents. Those GOP victories also helped Republicans gain control of the Senate.

“It doesn’t sound like much, one to two days, but when it is the last few days of the election, it is significant,” Commissioner Michael Healy said.

A spokesman for the Virginia-based Republican State Leadership Committee said the organization appreciated commissioners’ willingness to reduce the penalty.

“The RSLC maintains that we did not intentionally violate any provisions [of Maine’s law] and we have fully cooperated with the commission,” spokesman Adam Temple said.

The RSLC spent $398,970 on television and radio ads as well as mass mailings against five Democratic Senate candidates: Sen. Joe Perry of Bangor, Rep. Jim Schatz of Blue Hill, Sen. Deborah Simpson of Auburn, Rep. Pamela Trinward of Waterville and Rep. Patsy Crockett of Augusta.

The ads attacked the Democrats on a range of issues, including immigration, taxes and local politics. But because of the negative tone of the ads as well as their late arrival in the campaign, Maine Republican leaders as well as the GOP candidates in those races quickly distanced themselves from them and criticized the RSLC.

Under Maine’s campaign finance reporting rules, the RSLC should have disclosed that spending on Thursday, Oct. 21. But the organization did not file a report with the Ethics Commission until Saturday, Oct. 23 — a delay that several of the Democratic candidates said impaired their ability to promptly respond.

“What impact it really had on our races, we will never know,” Crockett said Thursday. “But the fact this money came in so late made it extremely difficult to deal with.”

A Maine-based attorney for the RSLC, Dan Riley, acknowledged that his client had filed the reports late. But Riley attributed the delay to a misunderstanding about Maine’s complex disclosure laws, which differ from those in other states where the organization has worked.

As a result, Riley urged the commission to lower the fine to between $10,000 and $12,000.

“There was an attempt to comply with the law,” Riley said. “They just did not understand the nature of the [disclosure] trigger here in Maine.”

Riley disagreed with statements that the candidates were significantly harmed by the late filing, pointing out that the Democrats had more than a week to respond to the RSLC ads. Even so, Riley said that RSLC officials were embarrassed by the content and quality of some of the ads, one of which even mispronounced the name of one of the candidates.

“There were a lot of things contained in those advertisements that they are not particularly proud of,” Riley said.

That mea culpa did not sit well with several commissioners as well as the complainants in the case, who pointed out that the RSLC ultimately was responsible for the content of the ads.

Simpson said the ads targeting her tried to capitalize on what she described as Republican-fueled fears and misinformation about Somali refugees living in her district. The Auburn Democrat called the ads “very personally damaging.”

Schatz, meanwhile, has filed a libel lawsuit against the RSLC and the advertisements’ creators. The lawsuit contends the ads and mailings made false and defamatory statements about Schatz regarding his time on the Blue Hill Board of Selectmen.

Based in Alexandria, Va., the RSLC describes itself as “the largest caucus of Republican state leaders in the country” with a mission to electing GOP candidates for governor, attorney general, secretary of state and the state Legislature.