SACRAMENTO — An effort to create a government-paid health care system for all Californians has morphed into a massive fight between Democrats at the Capitol and a nurses union, with insults, death threats and violent imagery of backstabbing directed at the legislative leader who pulled the plug on the bill.

In an unusual move, the Assembly Democratic caucus issued a statement Friday condemning what they called bullying tactics used against Assembly Speaker Anthony Rendon, D-Paramount (Los Angeles County). Rendon’s Sacramento and district offices reported receiving thousands of phone calls over the past few days related to the bill. Amid the uproar, Rendon said he and his family have received death threats over social media.

The fury directed at Rendon has been orchestrated by the California Nurses Association to pressure Rendon to allow the bill they are supporting to move forward with a legislative hearing. The nurses union adopted a slogan aimed at Rendon that said, “Inaction = Death.”

During rallies at the Capitol this week, nurses waved signs — one showing a picture of a knife with Rendon’s name on it plunged into the back of the bear on the state’s flag. At a union rally Wednesday in front of the Capitol, two people acted out the image with an oversized fake knife and a man in a bear costume.

With the unmistakable symbolism of the image, the union has accused Rendon of forsaking Californians and being in the pockets of insurance companies, who have lobbied hard against the bill.

“Lives are at stake in this issue,” said Charles Idelson, spokesman for the California Nurses Association, which is part of the 150,000 member National Nurses United union. “It’s unconscionable that the Speaker of the Assembly would abort the process ... without informing anyone — including our organization that is sponsoring the bill.”

Idelson said it’s the job of the Legislature to create laws, and if their bill needed more work, then lawmakers should come together to get it done.

Gavin McIntyre / gmcintyre@sacbee.com

Volunteers with the nurses union planned to fan out Saturday across Rendon’s district going door to door in hopes of building support for the bill among Rendon’s voter base. And nurses planned to return to the Capitol on Monday for another rally.

Even Democratic presidential runner-up Bernie Sanders jumped into the fray, urging Rendon in a tweet last week to reconsider his move to shelve the bill.

The nurses union said their members are not responsible for the death threats, and they do not condone the threats. They defended their aggressive campaigning to try to change Rendon’s mind, saying they do not believe their tone or tactics have been inappropriate.

But many lawmakers condemned what they saw this week. Assemblyman Jim Cooper, D-Elk Grove, said the bill’s proponents have incited violence.

“I am extremely disappointed and saddened that those who support an admirable cause have resorted to reckless, irresponsible and completely inexcusable actions to voice their opposition to a decision made by a leader in our state,” Cooper said in a statement.

Assemblywoman Lorena Gonzalez Fletcher, D-San Diego, wrote on Twitter: “I have always supported universal health care, but there is NO place for violent imagery or words in this debate. Period.”

Even other unions voiced concerns. Robbie Hunter, president of the State Building and Construction Trades Council, said the attacks on a “labor champion like Anthony Rendon” were “unfair and unwarranted.”

The fight has created a strange divide in the Capitol. The California Nurses Association and Democratic leaders in the legislature typically fight on the same side, for similar changes. This year, the union was pushing hard for a single-payer health system that had a hefty price tag — $400 billion a year — that had many Democrats raising questions about how the state would pay for it, even if they supported the concept of the bill.

Despite the unanswered questions, the state Senate passed the legislation 23-14 last month. When the bill reached the Assembly, however, Rendon said it was “woefully incomplete” and that the Senate needed to continue working on it before his house could vet it.

The bill, SB562, sought to create a universal health care system where the state’s 39 million residents would no longer pay premiums, deductibles or co-pays for health care services. The single government-run, universal-care system would replace the multi-payer system and upend the health insurance industry, which staunchly opposed the proposal.

While the bill’s author Sen. Ricardo Lara, D-Bell Gardens (Los Angeles County), had not come up with how the system would be funded, a Senate committee said a new 15 percent payroll tax could generate half of the $400 billion needed.

Lara has not publicly commented on the bill being pulled or the reaction to Rendon’s decision. He declined a request Friday to comment. Lara is running for state Insurance Commissioner, with the backing of the nurses union.

Lara has said the bill would ensure Californians don’t go bankrupt when they get cancer, that they don’t skip medical appointments to save money and that health care is not a privilege enjoyed only by those who can afford it.

Rendon said he supports that, too, and urged senators to continue working on the bill so that it answers the most basic questions — such as how the state would pay for it.

“SB562 is more a statement of principles than a genuine bill that actually does anything to create a single-payer health care system in California that covers everyone,” Rendon said in a statement. “The sponsors need to decide if they are serious about having a policy discussion about how to do this. Because a shell like SB562 certainly isn’t it.”

Rendon said he was most bothered by the nurses union telling voters that his decision to hold the bill will have catastrophic consequences. In one case Rendon said a parent told him, “You just killed my son,” because they fear their son, who needs a heart transplant, won’t be insurable with his preexisting condition under Republican proposals in Congress to replace the Affordable Care Act.

Rendon said the supporters of the bill touted their single-payer proposal as the answer for struggling Californians, but that they never provided answers on how it would work.

“It is shameful how the proponents of SB562 have provided false hope to people who are suffering,” Rendon said.

Melody Gutierrez is a San Francisco Chronicle staff writer. Email: mgutierrez@sfchronicle.com Twitter: @MelodyGutierrez