If the transportation funding proposal unveiled this week by Gov. Jerry Brown and state legislative leaders simply contained the gas tax hikes and vehicle fees outlined in their press releases and statements, then of course lawmakers should support the proposal. The state’s infrastructure needs far outpace the revenue collected in fuel taxes, which California has relied on for decades to pay for road repairs. More fuel efficient and electric vehicles on the road have reduced gas tax revenue has well. To close the gap, the common-sense proposal outlined by state leaders would raise fuel taxes and levy a new “road user fee” on drivers to pay for vital transportation infrastructure.

But the press releases and political speeches did not mention that the bill contains an unusual change from the leaders’ previous proposal. Added at the last minute at the trucking industry’s behest, it would block regulations that would force truck owners to upgrade to less polluting models. The addition says that regulators cannot directly or indirectly require owners to retire, replace, retrofit or repower their trucks within 13 years of the model year or when the vehicle hits 800,000 miles.

That amendment is a big concern in Southern California, where diesel-fueled big rigs are the region’s top source of smog-forming emissions. Regulators are trying to dramatically cut pollution from trucks that serve the region’s growing warehouse and distribution industry. The amendment also could make it harder for the ports of Los Angeles and Long Beach — the largest single source of air pollution in the region — to move to a zero-emission truck fleet.

California Air Resources Board Chairwoman Mary Nichols defended the change, saying she didn’t believe it would prevent Southern California regulators from developing rules to limit diesel pollution at warehouses. Environmental groups don’t buy it. They argue the provision is so broad that it could block the development of so-called indirect source rules that cap pollution at warehouses and indirectly force truck owners to switch to cleaner equipment.