The group that led a lawsuit against the IRS for illegally targeting conservative non-profit organizations celebrated the Justice Department's multi-million dollar settlement on Thursday.

Mark Meckler, president of Citizens for Self-Governance, hailed the $3.5 million settlement that came "after years of stonewalling." Citizens for Self-Governance spearheaded a lawsuit brought by a coalition of conservative groups that were subjected to enhanced scrutiny from the IRS delaying their approval for non-profit status. The plaintiffs asserted that the agency unconstitutionally policed their freedom of speech and harmed their chances of raising money in order to punish the Obama administration's political opponents.

"We all know the IRS unconstitutionally target tea party groups to shut down their political speech in a violation of the First Amendment. That has been unequivocally proven by the statements of IRS employees," he said in a statement. "After years of stonewalling by the federal government, the litigation against the IRS for their unconstitutional behavior has been settled and the targeted groups will receive substantial payments."

The IRS did not respond to request for comment.

Attorney General Jeff Sessions announced on Thursday that the Department of Justice had agreed to settle two lawsuits brought by 469 parties who were targeted by the IRS. He faulted the agency and the Obama administration for fostering a partisan application of the tax code and singled out the request for sensitive information, such as requests for donor lists, as irrelevant to making "a determination of tax-exempt status."

"It is now clear that during the last administration, the IRS began using inappropriate criteria to screen applications for 501(c) status," he said in a statement. "We hope that today's settlement makes clear that this abuse of power will not be tolerated."

Sessions said the IRS's approach to singling out conservative groups and prospective non-profits with "tea party" in their name distorted its mission. He called the agency's investigations "improper," adding that it "should never have occurred."

"It is improper for the IRS to single out groups for different treatment based on their names or ideological positions," he said. "Any entitlement to tax exemption should be based on the activities of the organization and whether they fulfill requirements of the law, not the policy positions adopted by members or the name chosen to reflect those views."

The settlement comes a month after the Justice Department announced it would not pursue charges against Lois Lerner, the IRS's director of the Exempt Organizations unit at the time of the scandal. Lerner and the agency stonewalled investigators and resisted public records requests by claiming that hard drive failures caused top officials to lose emails related to the controversy; the agency later admitted that it had in fact located those records. A 2013 inspector general report found that Lerner, who exercised her Fifth Amendment rights during congressional investigations into the scandal, and other senior Washington, D.C., officials were aware of the targeting as early as 2011.

Judicial Watch, a conservative watchdog group, called on the Trump administration to investigate the agency's conduct in its compliance with public records law, as well as its handling of conservative applications. Judicial Watch president Tom Fitton said he had "zero confidence that the Justice Department did an adequate review of the IRS scandal" in the wake of the September announcement.

"The FBI collaborated with the IRS and is unlikely to investigate or prosecute itself. President Trump should order a complete review of the whole issue," Fitton said in a release. "We await accountability for IRS Commissioner [John] Koskinen, who still serves and should be drummed out of office.

Meckler said he was pleased with the settlement and the "substantial" payments to IRS victims, but said the penalty should go beyond financial matters. He called on the agency to publicly apologize for breaching its constitutional duties to apply the law equally.

"The IRS still owes those citizens, and all of us, an apology," he said. "I will wait for it, but won't be holding my breath."

Sessions agreed that the agency should personally apologize for its actions.

"There is no excuse for this conduct. Hundreds of organizations were affected by these actions, and they deserve an apology from the IRS," he said.

The settlement will go into effect after it is approved by two federal district courts.