Three California lawmakers trying to cut local police pensions and other spending became the victims of a rogue opposition-research campaign in which union-backed investigators allegedly filed a bogus DUI report on one and illegally tracked all of them, according to a recently filed arrest warrant.

The case dates back to 2012 -- but the new court documents shed light on the flaring tensions at the municipal level over pension cuts, and the lengths to which unions and other opponents are going to fight them.

"This is just the beginning," Jim Righeimer, one of the targeted council members, told FoxNews.com. The FBI was involved in the case and helped create a Political Corruption Task Force, and Righeimer said they wouldn't have done that just to nab a couple of private detectives.

According to the Dec. 10 warrant documents, the incidents occurred in summer 2012 when Costa Mesa Council Members Stephen Mensinger, Gary Monahan and Righeimer were trying to cut police pension liabilities amid a bitter contract negotiation between the city and the local police union. Costa Mesa is pushing to cut police pensions to avoid following cities like Detroit and California's Stockton and San Bernardino, which went bankrupt in part because of pension costs.

Mensinger and Monahan also were seeking re-election that fall.

The court documents detailed the evidence that led Orange County prosecutors to file criminal charges against the investigators, Chris Lanzillo and Scott Impola. They were working for a now-defunct law firm that had been hired by the police union -- though investigators say the union was unaware of the rogue operations.

Investigators alleged that on Aug. 22, the two tried to lure Monahan into compromising behavior by sending a female "operative" wearing a top "exposing her cleavage" into his bar-restaurant, Skosh Monahan's.

Lanzillo and Impola were charged with one count each of false imprisonment, conspiring to file a false police report and conspiring to and unlawfully using an electronic tracking device.

The first two charges are connected to incidents that allegedly occurred the night of Aug. 22, the same night Lanzillo and Impola purportedly tried set up Monahan with the woman.

Lanzillo reported seeing Righeimer stumble outside Skosh Monahan's, then drive home erratically, either intoxicated or disabled.

Police arrived at Righeimer's house and temporarily detained him, until administering a sobriety test that showed he was not intoxicated.

According to the court documents, Righeimer's wife confronted Lanzillo outside their house as he was driving away, and told him he was "probably a union bully." Investigators later accused Lanzillo of "falsely reporting" the DUI that night.

The third charge is in connection with Lanzillo allegedly buying a GPS tracking device, under a false name, then using it with Impola to illegally tail vehicles belonging to Mensinger -- now the city's mayor -- and Monahan.

Investigators say records show the device "pinged" at or near the homes of both private investigators, Mensinger, Monahan and Righeimer, from June through August 2012.

Efforts to locate the private investigators for comment were unsuccessful. According to an article in U-T San Diego, Lanzillo initially issued a press release saying he was on assignment when he was at the bar and couldn't give details about that assignment.

With help from the FBI, prosecutors used such evidence as computer activity, search warrants, video and audio tapes and money transactions -- including bank checks and credit card accounts -- in their two-year probe that ties together the union, the investigators and the law firm Lackie, Dammeier, McGill & Ethir. Lanzillo and Impola each used American Express cards issued by the firm.

Though the union may not have been aware of the tactics used, they allegedly wanted the firm to dig up dirt on targeted politicians. The union, the Costa Mesa Police Officers Association, appeared to increase dues to pay the firm for the opposition research, according to the 31-page warrant filing.

In one email, a union official suggested telling the law firm that Righeimer and Mensinger would soon be in Las Vegas where they might engage in secret, illegal meetings with developers and that he could "totally see [Mensinger] sniffing coke of (sic) a prostitute."

In addition, the law firm, which has not been charged in the case and represented roughly 120 other police unions before shuttering last year, posted on its website a "playbook" on opposition research.

Among the suggestions were to "focus on a city manager, council person, mayor or police chief and keep the pressure up until that person assures you his loyalty and then move on to the next victim," according to the documents.