The National Legal and Policy Center (NLPC), a conservative watchdog group, on Monday filed a complaint with the Federal Elections Commission (FEC) accusing Rep. Maxine Waters (D-CA) of violating federal election laws earlier this year.

According to the NLPC, Waters' campaign sent out a "slate mailer" that included former Los Angeles Mayor Antonio Villaraigosa who was running for Governor in the Democratic primary. Villaraigoa's campaign agreed to pay a $25,000 fee for the mailer. NLPC says Villaraigosa failed to pay for the mailer but a group called "Families and Teachers for Antonio" paid the fee.

"Whereas candidates like Villaraigosa may legally pay Waters' campaign for the proportional costs of their inclusion on her slate mailer, it is not legal for such payment to be made by a third party like 'Families and Teachers for Antonio,'" NPLC alleges.

NLPC filed a similar complaint with the FEC for another "slate mailer" which was part of the 2016 election. The watchdog group says Waters' campaign accepted $35,000 from the Democratic State Central Committee of California (DSCCC) to include then-Senate candidate Kamala Harris.

Waters has been sending out "slate mailers," which resemble a sample ballot distributed by political parties before an election, for years.

According to the FEC's 2004 advisory opinion, payments from other candidates "would not constitute support of, or in-kind contributions to, any federal candidate appearing in the brochure, so long as the authorized committee of that federal candidate reimburses the Waters Committee."

"She pioneered a new way to use slate mailers by seeking an Advisory Opinion from the Federal Election Commission in 2004 that allows her to use her federal campaign to also function as a State of California slate mailer committee while still maintaining eligibility as a principal federal campaign committee," NLPC said.

Walters' campaign raised more than half of her 2010 campaign funds from these mailers, the Sunlight Foundation previously reported. And it's a practice she has continually kept.

NLPC has requested the FEC investigate the alleged violations as well as an audit of Waters' campaign committee.

"Since the commission has given federal campaigns broad discretion involving slate mailers it is imperative the issues cited in this complaint are fully investigated and all penalties and fines that may result from a finding that the Citizens for Waters campaign was in violation of the statutes cited should be applied in full,” the complaint said, Fox News reported.

“In the advisory opinion the Commission clearly states that payments made to the Citizens of Waters campaign by candidates is a reimbursement to the Waters campaign for costs related to the slate mailer the campaign creates for elections,” the complaint continues. “These reimbursements allow candidates to exceed campaign finance contribution limits. Since this money did not come from the candidate, Antonio Villaraigosa, or any campaign or agent of Mr. Villaraigosa this payment cannot be considered a reimbursement by the candidate, candidate campaign or agent of the candidate to the Citizens for Waters campaign committee.”

To make matters even more interesting, Waters has paid her daughter Karen Waters, or her progressive public relations firm Progressive Connections, to produce, print and send the mailers. Waters has faced scrutiny over this issue since 2010.