The Tennessee Senate on Thursday approved a nearly $2 billion tax and refund for businesses, a proposal designed to prevent threats of a potential lawsuit even as critics warned the so-called solution was rushed without being properly vetted and shrouded in mystery.

Starting last fall, Republican legislative leaders say a law firm representing a large group of businesses contacted the state to question the legality of Tennessee’s 90-year-old franchise tax and demanded a refund. In response, Gov. Bill Lee initially proposed offering businesses $1.2 billion in refunds and then an ongoing $410 million in tax breaks.