Alabama in 2024 became the first state to carry out a nitrogen gas execution. Now, at least two states are looking to follow in its path.

A death row inmate slated to become the first person to be put to death by nitrogen gas in Louisiana is seeking to halt the execution, citing constitutional concerns over the controversial killing method.

Louisiana officials have unsealed a redacted version of the state’s execution protocol for nitrogen hypoxia, providing the first public look at how the state plans to carry out its first execution in nearly 15 years.

Arkansas currently only allows executions by lethal injection. If this bill becomes law, the state would join a small group of others permitting nitrogen hypoxia.