(Image Credit: Susan Walsh/AP Photo)

At least the third tea party-affiliated organization alleging unfair scrutiny by the Internal Revenue Service has filed a federal lawsuit on behalf of tea party and conservative groups against the IRS, U.S. Attorney General Eric Holder, Treasury Secretary Jack Lew and various IRS officials.

One of the 25 conservative groups in the suit filed today is the Waco Tea Party, run by president Toby Marie Walker, who told ABC News she's "a little nervous" of retaliation, but knows it's the right move.

"It makes you a little nervous, but I believe we have great attorneys that will represent us well and this is the time for Americans to put government back in its constitutional box and not allow them abusive power on their citizens," Walker said, adding, "I do feel like this will be a landmark case that people will talk about for years to come."

Acting IRS Commissioner Steven Miller, who was forced to resign amid the scandal, and IRS director of Exempt Organizations Lois Lerner, who has been placed on administrative leave after she reportedly refused to resign, are among the targeted IRS officials.

Jay Sekulow, chief counsel for the American Center for Law & Justice, said, "The IRS and the federal government are not going to get away with this unlawful targeting of conservative groups."

"As this unconstitutional scheme continues even today, the only way to stop this flagrant and arrogant abuse of our clients' rights is to file a federal lawsuit, which we have done," Sekulow, who worked as a tax trial attorney in the 1980s in the Office of the Chief Counsel for the IRS, said in a statement. "The lawsuit sends a very powerful message to the IRS and the Obama Administration, including the White House: Americans are not going to be bullied and intimidated by our government."

The ACLJ and its 25 conservative groups join at least two other groups that have filed suits: True the Vote and the NorCal Tea Party, both of which filed last week.

Of the 25 groups the ACLJ is representing, 13 organizations received tax-exempt status after what they say were "lengthy delays," 10 are still pending and two withdrew applications because of what they say was frustration with the IRS process.

The suit also names Holly Paz, director of the IRS Office of Rulings and Agreements, as well as "unknown named officials inside the IRS," and is seeking a judgment that the defendants violated the First and Fifth Amendments to the Constitution that meant "unlawfully delayed and obstructed Plaintiffs' applications for a determination of tax-exempt status by means of conduct that was based on unconstitutional criteria and impermissibly disparate treatment."

The complaint alleges the defendants "unlawfully delayed and thereby effectively denied approval of Plaintiffs' applications for tax exempt status by means of a comprehensive, pervasive, invidious and organized scheme that purposefully established unnecessary and burdensome inquiries and scrutiny of Plaintiffs' applications based solely upon Plaintiffs' political viewpoints."

The complaint says the evidence they have of "unlawful conduct" by the listed defendants include details asked of on the questionnaires including "excessive scrutiny of Plaintiffs' applications by requiring donor names, listing of issues important to Plaintiffs' organizations, including their positions on such issues, the contents of communications between the organizations and legislative bodies, the applicant's criteria for membership, volunteer names and the political affiliations of persons associated with the organizations."

The 10 groups that have not received tax-exempt status are asking for it to be given to them and the groups are also seeking financial damages to be determined at trial at a later date. The suit also seeks "injunctive relief to protect" the groups "from further IRS abuse or retaliation."

In an interview with ABC News last week, Sekulow said "the admission and apology by the IRS that the criteria used [in tea party applications] was not correct and inappropriate" and is grounds for a suit. He also said the conservative groups he represents are "still getting letters requesting information" and, he believes, "if we don't file suit, we won't bring an end to this."

The ACLJ says more groups are "likely to be added" as the lawsuit progresses.

The IRS said it is unable to comment on "pending litigation so we won't be able to comment on" the ACLJ's lawsuit.

ABC News' Abby Phillip contributed to this report.