Tesla Motors wants to sell its electric-powered cars directly to consumers.
Missouri auto dealers want to protect their "franchise agreement" law, which requires car manufacturers to work with a dealer.
Tesla now is decrying what it considers a last-minute legislative move to protect traditional car dealers and prohibit direct car sales to consumers.
The Senate last Wednesday approved language changes to a House-passed bill that included the franchise agreements.
The original, House-passed bill only had changed the state's definition of an all-terrain vehicle.
Unless the House accepts the Senate's language, the different versions must be worked out in a conference committee - and Senate President Pro Tem Tom Dempsey said Monday evening that's the way it should happen.
"I support all of our auto dealers and manufacturers playing on the same playing field," Dempsey told reporters. "If we want to talk about the three-tier system that we have, and why the state of Missouri has a three-tier system, I think that's the right way to have that discussion."
As he explained the bill last week, Senate sponsor Jay Wasson, R-Nixa, told colleagues: "The car dealers a short time ago, some time ago, felt like there was some ambiguity in their franchise agreements.
"This language basically just says that, if you are an auto manufacturer, and those goods are being sold in this state, they will be under the franchise agreement and sold by a franchiser."
The language was added in a Senate committee substitute after Transportation Committee Chairman Mike Kehoe, R-Jefferson City and a veteran car dealer, last month asked the Revenue department why Tesla was licensed in 2013 to operate a sales operation near St. Louis, even though it had not contracted with any dealers.
Tesla's business model is "clearly designed to circumvent the traditional franchise model for the distribution and sale of new motor vehicles," Kehoe said in the letter.
On April 30, Acting Revenue Director John Mollenkamp wrote: "It is not clear that the statutes apply to a seller like Tesla."
The Senate passed the bill, with the revised language, a week later, on a 28-3 vote.
During their debate last Wednesday, no one questioned the language about car dealer franchises.
Instead, they spent a few minutes discussing a different change in the House bill, that allows Missouri motorcycle dealers to be open on Sundays.
In a Monday afternoon news release, Missouri Auto Dealers Association President Doug Smith urged lawmakers to accept the Senate-added language.
"For more than 30 years, Missourians have purchased their vehicles through our current franchise system which protects consumers and promotes market competition," he said. "Recently, Tesla Motors has used a loophole in the law that has allowed them to sell their cars with an unfair competitive advantage that strips the consumer protections that have been in place."
In the House, Judiciary Committee Chairman Stan Cox, R-Sedalia, and Rep. Chris Kelly, D-Columbia, issued a joint news release saying the "shortsighted measure" the Senate passed could make it more difficult for Missouri to attract to new business and industries.
"Regulations are desirable in circumstances where consumers need to be protected, not for shielding the powerful from the free market," Kelly said.
Dempsey predicted that, with the constitutional mandate that lawmakers end the session at 6 p.m. Friday, "If an amendment is added, I suspect that will kill the bill."