Modifies provisions of the "SALT Parity Act"

HB 3405 modifies Missouri's tax treatment for partnerships and S corporations (referred to as "affected business entities"). It imposes a new tax on these entities doing business in Missouri, calculating the tax by adjusting their federal income (after state deductions) or applying a 20% deduction to ordinary business income for tax years starting in 2027. The tax applies to income sourced within Missouri, with losses allowed to be carried forward to future tax years. This directly affects Missouri-based partnerships and S corporations, particularly those with members holding interests through multiple tiers.