SAN JOSE -- The two main special interests in San Jose politics -- organized labor and big business -- are hoping to steer the mayor's race in their direction by pouring serious cash behind their preferred candidates, igniting renewed concerns that rich groups are bypassing the city's campaign contribution limits.

With the race to replace termed-out Mayor Chuck Reed coming to a head at Tuesday's primary -- where the top two candidates are expected to advance to a November runoff -- voters are getting bombarded with last-minute mailers and other advertisements.

But an analysis by this newspaper found many of the ads are not coming from the candidates themselves but political action committees, or PACs, that are spending independently. The PACs are so aligned with the candidates in other ways, though, that critics and even the mayoral contenders fear the special interests will too strongly influence the eventual winner.

In all, outside groups have laid down more than half a million dollars in independent expenditures in the mayoral campaign, or about one-fourth of all the $2.1 million in total political cash spent in the race.

For 34 years, San Jose has had laws that try to limit political spending in its mayoral and City Council races. In this year's primary, no one can give more than $1,100 directly to any mayoral contender, and all the candidates have agreed not to spend more than $795,000.

But the candidates' own campaigns are now just part of the picture. A series of court decisions going back to the last open San Jose mayoral race in 2006, most notably the 2010 U.S. Supreme Court ruling in the Citizens United case, allows unlimited cash to flow through independent expenditure committees.

"Our hands are pretty much tied," said Vice Mayor Madison Nguyen, a mayoral candidate who hasseen two competitors benefit strongly from PAC spending.

A PAC backing Councilman Sam Liccardo has received nearly $240,000 from a group of local CEOs and other business leaders -- many from outside San Jose. That's on top of the nearly $800,000 Liccardo had already raised in direct contributions -- largely from businesses -- giving him significantly more money than any other candidate.

The rest of the PAC money has gone to support Santa Clara County Supervisor Dave Cortese. His mayoral bid has gotten a $245,000 boost from local unions such as police officers and firefighters. Included in the tally are $50,000 from the city's two casinos, forbidden by San Jose law from donating directly to candidates. That's on top of the $567,000 in direct contributions Cortese has received, much of which also came from unions.

"I think it's important for a critical voter to ask: What is this contributor expecting?" Liccardo said. "I see a list of tech leaders in the valley supporting (me) and a group of card clubs and unions with very significant interests at stake in City Hall investing in" Cortese.

Cortese, who notes his business background in saying he's not a union pushover, pointed to the list of non-San Jose residents giving money to the PAC backing Liccardo and retorted: "We don't want the city run by outsiders or carpetbaggers."

Cortese and Liccardo insist they oppose large independent expenditures in general and have no connection with the PACs, which must by law operate independently of the candidates' campaigns. But in some cases it's hard to tell the two apart.

Filings by the union PAC show tens of thousands of dollars spent on food, supplies and office space for Cortese supporters who call voters and knock on doors for him. And the leader of the PAC supporting Liccardo is Silicon Valley Leadership Group CEO Carl Guardino, a close friend of Liccardo's.

Ben Field, the South Bay Labor Council PAC director, declined an interview request but said in a short statement that his "grassroots" group depends less on money than other forms of support.

Guardino says he and a handful of allies started the PAC only to counter the union money expected to come in for Cortese.

"We wanted to see if we could at least somewhat balance that playing field," Guardino said.

While unions have historically been the biggest spender in mayor's races, Guardino's PAC pushed total funds supporting Liccardo past $1 million, while Cortese has about $800,000 in combined PAC and direct funds backing him. The three other contenders -- Nguyen and council members Rose Herrera and Pierluigi Oliverio -- have no PAC money and less than half a million dollars each in direct funds.

But having the most money doesn't always equal success. The last time the mayor's seat was open, in 2006, nearly $1.5 million in direct and PAC funds came in for labor-backed candidate Cindy Chavez in the November runoff, almost twice the money supporting her opponent, Reed. The big difference between the two was all the independent expenditures supporting Chavez. Yet Reed easily won.

Oliverio, for one, has singled out his opponents as "special interest candidates" in promoting his platform, which he says is truly independent because he's only taken money from individuals.

"At the end of the day if (PACs) are giving that kind of money, will you hold yourself accountable to special interest groups or to constituents?" Nguyen asked.

Contact Mike Rosenberg at 408-920-5705. Follow him at Twitter.com/rosenbergmerc.

Independent expenditures in the San Jose mayor's race
Supporting Dave Cortese
South Bay Labor AFL-CIO Labor Council Committee on Political Education: $162,658 as of Wednesday
San Jose Firefighters, IAFF Local 230 PAC: $36,067 as of May 17
San Jose Police Officers Association PAC: $31,776 as of May 9
Santa Clara County Government Attorneys Association PAC: $9,389 as of May 9
Association of Retired San Jose Police Officers and Firefighters PAC: $5,856 as of May 17
Total: $245,746
Opposing Dave Cortese
California Apartment Association PAC: $59,906 as of Tuesday
Supporting Sam Liccardo
Citizens for a Safe & Strong San Jose, supporting Liccardo for Mayor 2014: $239,468 as of Wednesday
Source: City clerk's office. Dates and figures represent most recent reports filed by the groups.