SAN PABLO -- While politicians, labor leaders and large institutions have poured money into the mail-in ballot campaign to pass a parcel tax for Doctors Medical Center, two deep-pocketed local property owners have spent $27,500 in campaign mailers to try to defeat the tax.

Richard Poe and Mark Howe, who each own hundreds of thousands of square feet of rentable commercial space in the district, have used their funds on production and distribution of mailers to the district's roughly 100,000 likely voters, urging them to vote no on Measure C, which would levy a 14-cent per square foot tax on developed property.

"What we have is two major property owners in the area who have decided to fund an opposition campaign," said Contra Costa Supervisor John Gioia, who also sits on the board of the health care district that operates the hospital. "It's their right to do what they want with their money."

Voters in the West Contra Costa Health Care District are already mailing in their ballots for the May 6 parcel tax, which supporters say is needed to keep open the area's only public safety-net hospital. The ballot measure needs two-thirds voter approval to pass and would go into effect in July if approved.

Measure C would generate an estimated $20 million annually for the hospital, which is hemorrhaging about $1.5 million every month despite cost-cutting and new revenues that have cut the operating deficit in half in recent years.

While more than $400,000 has poured into the pro-tax campaign, mostly from Kaiser Permanente and the San Pablo Lytton Casino, the opposition money that began rolling in this month could be a major impediment to passage because voters in the district already shoulder some of the highest property tax burdens in the state.

"I think government spending is wasteful and suspect the hospital district is trapped in the same spending pattern," Howe wrote in a letter to Gioia. "So I am suspicious and jaded when the hospital district asks me to pay for another tax."

Poe, who owns extensive real estate in Richmond's Marina Bay district, said he would be "happy to pay the tax" if not for doubts about the hospital's long-term viability. Like Howe, he wants deeper cuts to hospital operations rather than taxes.

Howe, who says he leases properties to 75 small business tenants, estimates the tax will raise his property tax burden from $135,000 to $180,000 annually.

"It is a struggle to save every month for these taxes," Howe wrote.

Chevron Corp. which runs the state's second-largest oil refinery in Richmond, would be the single biggest taxpayer if Measure C passes, with its square footage yielding about $350,000 annually. Chevron has kicked in $20,000 to the pro-Measure C campaign.

"We are donating in recognition of the crucial role the hospital plays in serving the West County community," Chevron spokeswoman Melissa Ritchie wrote in an email.

Adding to the mounting opposition to Measure C is the reality that while it should wipe out the operating deficit, the hospital's long-term future is uncertain, a fact that is not divulged in most of the pro-C campaign mailers.

The hospital faces a looming 2020 state deadline to retrofit its facilities for earthquake safety, a mandate that has been pushed back before but could mean the need for $40 million to $60 million in repairs.

Hospital CEO Dawn Gideon defended the pro-C campaign, to which she has donated $1,000.

"I think we've been pretty clear all along that we have seismic challenges in the future," Gideon said.

Gioia and district board Chairman Eric Zell downplay those concerns, saying the goal now is to save the hospital with Measure C and put it in position for a range of long-term viability solutions.

"Our goal is eventually to build a new, smaller hospital that West County deserves by setting aside capital reserves, partnering with another health care institution and using the proceeds from the sale of the property," Gioia said.

Zell said at a community event this week that a future bond measure may be "part of the plan" for long-term viability of DMC.

Opponents say Measure C, which follows two smaller voter-approved parcel taxes to save the hospital in the past decade, is not the end of DMC's money drive. They speculate the hospital board will seek a bond measure in a future election.

Gioia and Zell don't deny that is possible but say coming back for more money is unlikely.

"I can say we will not be coming to the voters this November for more money," Gioia said.

But the new, smaller hospital is a key point in anti-C campaign mailers paid for by Poe and Howe. In one that hit mailboxes this week, anti-tax advocates say Gioia and the rest of the board have already decided to tear down DMC and build a $140 million replacement facility, a claim Gioia denies.

"It's irresponsible that two wealthy real estate developers care more about their profits than the health care needs of West County residents and are lying to voters about the facts regarding the hospital," Gioia said.

Wendy Lack of the Contra Costa County Taxpayers Association, which opposes Measure C, said it's no surprise that some money has emerged in opposition to the tax.

"Naturally, the big corporate interests won't oppose powerful political interests like Gioia and Zell," she wrote in an email. "But one assumes the small business owners feel they have nothing to lose."

Contact Robert Rogers at 510-262-2726 or rrogers@bayareanewsgroup.com. Follow him at Twitter.com/SFBaynewsrogers.