The Texas governor had not publicly shared his thoughts on the actions of a bipartisan group of lawmakers that stopped the scheduled execution of Robert Roberson.

The three-page letter sent Sunday by James Sullivan, Abbott’s general counsel, said only the governor has the constitutional authority to delay an execution. Sullivan warned that unless the court rejects the subpoena, “it can be repeated in every capital case, effectively rewriting the Constitution to reassign a power given only to the Governor.”

Death row inmate Robert Roberson is expected to testify before Texas state lawmakers after his execution was halted last week.