The chamber announced its endorsement of Amendment 7 Thursday.
The three quarter cent sales tax would raise nearly $500 million for transportation projects a year for the next 10 years.
The tax would pay for 135 road and bridge projects in northwest Missouri including improvements at the 36 Highway and Riverside intersection and I-29 and south 169 interchange in St. Joseph.
The chamber says those two projects could pave the way to more business in St. Joe.
"Both interchanges are very congested and not only are detrimental to future growth in those areas but also are safety factors," said St. Joseph Chamber of Commerce President & CEO Patt Lilly.
The tax will be up for vote during the August 5 primary.