JEFFERSON CITY - Although the U.S. Supreme Court affirmed the constitutionality of the new federal health care law, Missouri voters will get to cast ballots in November on another of the law’s key components -- insurance exchanges.

Proposition E on the November ballot would prohibit Gov. Jay Nixon or any state agency from setting up a health insurance exchange without the approval of the legislature or the state’s voters.  

A health insurance exchange is a Web-based marketplace for consumers to compare insurance plans. The exchanges are a central part of the federal law because they are intended to help individuals and small businesses purchase insurance at an affordable rate to comply with another part of the federal law that mandates most people own health insurance.

Nixon has said in the past that his administration would not move to set up an insurance exchange by decree. But some Republican legislators say they want to make sure the Democratic governor is barred from doing so if he wins a second term, especially after the U.S. Supreme Court upheld the law in a 5-4 decision on June 28.

And tea party groups, which have strongly opposed the federal law, have signaled their support for Proposition E as a way to stave off its implementation.

But Ron Staggs, who heads the group "9-12 We The People of Monroe County" with his wife, said he expects many of his members to turn out against a law they consider anathema.

"By blocking the governor and the Insurance commission without a vote from the legislature, ObamaCare can be effectively blocked in the state of Missouri,” Staggs said in a phone interview.

That block would only be temporary. The federal law requires there to be an exchange in every state by 2014—even if it means that federal authorities have to set up an exchange without a state's permission.

That requirement is one of the reasons Proposition E has not gotten as much attention as Proposition C, a measure on the August 2010 ballot that would bar the government from mandating that people purchase insurance, another central tenet of the federal law.

Missouri voters backed Proposition C by a more than 2-to-1 margin in 2010. But at the time, the constitutionality of the federal law was still being weighed by courts around the country.

The U.S. Supreme Court’s ruling, however, makes it nearly certain that the requirement for health care exchanges will take effect unless congressional Republicans manage to repeal the law.

That has groups who supported the law, such as Missouri Health Care for All, saying that Missouri should simply prepare its own exchange.

"Prop E is really just an attempt to continue to use health care reform for political gain because there's really going to be no practical effect because health reform, the Affordable Care Act, is the law of the land,” said MHCA President Susan Talve, a St. Louis rabbi, in a telephone interview.   

This year’s ballot measure did garner attention throughout the summer as conservative politicians challenged ballot summary language crafted by outgoing Democratic Secretary of State Robin Carnahan, who is not running for re-election.

Carnahan’s original summary asked whether state law should be amended to “deny individuals, families, and small businesses the ability to access affordable health care plans” through an insurance exchange, phrasing that Republican lawmakers and Lt. Gov. Peter Kinder immediately decried as partisan.

Late last month, a Cole County circuit court judge revised the summary language to say that the governor would be blocked from creating the exchange by executive order.

Not all Republicans are opposed to the creation of a state health insurance exchange. In 2011, state Rep. Chris Molendorp sponsored legislation to set up such a marketplace. The measure passed with no opposition in the state House, but hit a wall in the Senate. 

In pushing his measure last year, Molendorp said that setting up an insurance exchange could take a year or more, so Missouri needs to start the process soon if it wants to have its own exchange in time to meet the federal deadline.

Molendorp, R-Belton, handled in the House the legislation that created Proposition E.

In an interview on the sidelines of the legislative veto session earlier this month, he said that if voters approve the measure, the legislature should craft the state’s exchange themselves rather than waiting for federal action.

He said Missouri’s insurance market has many factors that make it too unique for federal rules, including the disparities between the state’s two large metropolises and its many rural areas.

"We have, I think, a very legitimate reason to set up our own unique exchange tailored to the complexities of the Missouri health care and the Missouri insurance market,” he said.