Substitute Senate Bill No. 1558, now Public Act No. 25-172, mandates the Attorney General to study and report on measures to protect Connecticut residents from income taxes imposed by other states or the District of Columbia on income earned while residing in Connecticut. The report, due by January 1, 2026, will include findings and recommendations for the General Assembly's finance committee.

Additionally, the bill introduces a new tax credit for Connecticut residents who have paid income taxes to other jurisdictions. This credit, effective for taxable years starting January 1, 2020, allows eligible residents to claim a credit equal to 60% of the taxes owed to Connecticut due to adjustments in credits for taxes paid to other states. To qualify, residents must meet specific criteria, including having paid taxes to another state, being denied a refund, appealing that denial, and receiving a final decision that results in a tax refund. The bill also stipulates that no penalties or interest will be imposed on late tax payments if they are due to a reduction in the credit resulting from a refund from another jurisdiction.