To the tax-weary audiences at Gov. Christie's town halls, it is a gasp-inducing concept: public workers cashing in unused sick days for lump-sum payments so large that towns must take out bonds to cover them.

The Republican governor has made ending the practice his key goal in recent months, repeatedly railing against the perk at public forums. He has garnered the support of 234 mayors from both parties and won over crowds with tales of workers who allegedly traded in their accrued time to buy boats.

But the issue is not as black-and-white as Christie makes it sound, and the dollar figures he drops to make his case are based on estimates, worst-case scenarios, and old data.

Nearly a quarter of New Jersey's 566 municipalities do not have employees eligible to collect sick-leave payouts, according to the state's own list. And many towns and a few school districts have eliminated the perk or do not have it in their collective-bargaining agreements.

On the stump, Christie tells taxpayers that they would be on the hook for $3.25 billion if Democrats in the Legislature defy him and instead cap sick payouts for current workers at $7,500.

Yet that figure - $7,500 for each of the more than 400,000 current state and local employees - assumes that all workers are old enough (at least 55) and will be employed long enough (up to 30 years) to become eligible, based on a review of union agreements. It requires that they have stayed healthy and accumulated the maximum sick time.

And it posits that every collective-bargaining contract allows a $7,500 payout. Many local governments forbid cashing in the time, and some that do have caps lower than $7,500. For example, 28 percent of school districts cap payouts below $7,500, according to the New Jersey Education Association teachers union. Others have an aggregate cap on what will be paid in a given year.

Though acknowledging that the governor's $3.25 billion number is "admittedly imprecise," it is not inaccurate, said Michael Drewniak, Christie's spokesman. It is "an illustrative figure only," he said.

Because it represents a moment in time - for the current cohort of employees, not the hundreds of thousands hired in years to come - the long-term obligation will be far greater, Drewniak said.

"It does not come close to the full universe of public employees in New Jersey and does not account for employee growth and turnover," he wrote in an e-mail.

Local governments also could adopt more generous policies, noted Thomas Neff, head of the state Division of Local Government Services. He cited Old Bridge, Middlesex County, which recently loosened its limit on lifetime medical benefits to allow more employees to qualify.

To sell his "use-it-or-lose-it" policy and frame Democrats as beholden to unions and "special interests," Christie has launched his attack from the territories where he has waged other legislative battles: town halls, press events, and social media.

He has a slogan: "Zero means zero."

His campaign seems to have softened Democratic opposition. A compromise bill recently introduced by Assemblywoman Pamela Lampitt (D., Camden) would ban cash payouts but allow retiring workers to use up to $7,500 in unused sick time toward future health premiums.

It is unclear if that legislation will go to the governor's desk in the final day of the legislative session on Jan. 9.

John Wisniewski, an assemblyman and state Democratic chairman, called Christie's numbers "speculative."

"That's how this governor operates," he said.

Christie's outrage resonates among those in New Jersey's private sector, where 38 percent of workers receive no paid sick time at all, according to the Institute for Women's Policy Research.

At a Monroe Township town hall meeting in May - in a sound bite viewed more than 20,000 times on YouTube - Christie didn't say the $3.25 billion figure was "imprecise" or "illustrative."

He spoke of it as fact: "If I signed a bill for a $7,500 cap, you know what the bill would be? The bill would be $3.25 billion. . . . There's no justification for paying people cash for not being sick. Only in government would we be doing something like this."

Christie's Facebook page and the Senate Republicans' website have calculators allowing New Jerseyans to look up their towns' sick-leave obligations. Municipalities such as Haddonfield that do not have a sick-leave liability are omitted without explanation.

Christie says New Jersey towns' sick-pay liability is $825 million for employees eligible to cash out now. That number is accurate, but it is based on 2010 budgets, not the most recent data available, according to the Department of Community Affairs.

In Cherry Hill, sick-leave payouts were banned for unionized employees in the 1980s and for noncontractual employees in 2007. The township's current $500,000 obligation is the maximum available to employees grandfathered in under the old system; it will dwindle to zero after those employees retire.

State employees represented by the largest state union have their leave payments capped at $15,000, which includes unused vacation time accrued over a year. One unused sick day equals a half-day of pay at retirement.

"This is a retirement benefit," said Hetty Rosenstein, state director for the Communications Workers of America, who notes that all the payouts were negotiated. "Everyone isn't eligible for it."

Nationwide, just 6 percent of employers have a sick-leave cash-out option, according to the Society for Human Resource Management.

The benefit is more common in government. In Philadelphia, retiring city workers can get cash for accumulated sick time, depending on when they leave and what work they do. In some cases, the accrued leave can be used to buy retiree health coverage.

Like Philadelphia, Pennsylvania state government does not cap cash payouts on unused sick leave. But it limits how many days can be carried over per year. In fiscal year 2010-11, according to the state's Office of Administration, 3,393 employees cashed in more than 1.4 million hours worth $49.6 million.

In recent months, states including Ohio, Arizona, and Florida also have grappled with retiring employees drawing large checks for sick time.

Christie says New Jerseyans have long known that the payments were a problem. Since at least 1996, state reports have cited massive payments to retiring Camden employees. Between 2004 and 2008 alone, $3.6 million went to 159 new retirees for unused leave and severance pay. Most of it, $2.3 million, went to 20 people, according to a Commission of Investigation report. The employees also received pensions.

Christie often cites the example of four high-ranking police officers in Parsippany, Morris County, whose lump-sum sick-time payments amounted to $900,000. Rosenstein said these higher-paid supervisors are the problem, not rank-and-file workers.

"Let's deal with the issue honestly . . . without the hyperbole, without having it be propaganda or demagoguery," she said.

Charles DeCicco, 63, who retired last year after 37 years as a Medicaid supervisor for Atlantic County, said the sick-leave payment was one reason he took the position. The Hammonton resident made a $60,000 salary in his final year, and took $7,000 for accrued sick leave.

"That was one of the perks of the job. It certainly wasn't the salary," he said. "The taxpayers didn't get ripped off by me."

Contact staff writer Matt Katz at 609-217-8355, mkatz@phillynews.com, or @mattkatz00 on Twitter. Read his blog, "Christie Chronicles," at philly.com/christiechronicles

Staff writers Miriam Hill and Angela Couloumbis contributed to this report.