Conn. Gen. Stat. § 12-216: Payment of tax by out-of-state corporations.

The tax imposed by this part upon corporations or associations carrying on or doing business or having the right to carry on or do business in this state, which corporations or associations are organized and exist under and by virtue of the laws of some other state, territory or country or are organized and exist without any specific statutory authority, shall be paid by such corporations or associations for the benefit and protection of the government and laws of this state, it being the purpose of this section to require the payment of a tax by all corporations or associations carrying on or doing business in this state, but not organized under the laws of this state, as an additional recompense for protection of the activities in this state of such corporations or associations.