For years, fossil fuel producing states have watched investors shy away from companies causing the climate crisis. Last year, one state decided to push back.

Texas passed a law treating financial companies shunning fossil fuels the same way it treated companies that did business with Iran, or Sudan: boycott them.

"This bill sent a strong message to both Washington and Wall Street that if you boycott Texas energy, then Texas will boycott you," Texas Representative Phil King said from the floor of the Texas legislature during deliberations on the bill, SB 13, last year.

But the Lone Star state is straining to implement the law. Loopholes and exceptions written into the law could sap its impact on financial firms that have aggressive climate policies.

This March, the Texas State Comptroller began sending letters out to financial institutions, probing their climate policies. Leslie Samuelrich, president of Green Century Capital Management, a fossil fuel-free mutual fund, says her firm recently received its letter.