(RNS) As Supreme Court Justice John Paul Stevens prepares for retirement, religious advocates are cheering his support of church-state separation and readying for the battle over his successor.

Stevens, the court’s oldest justice at age 89, sent a letter to President Obama Friday (April 9) informing him that he would retire when the high court concludes for this year’s summer recess.

“Justice Stevens is an icon — a thoughtful, perceptive justice who understands the role of church-state separation in American life,” said the Rev. Barry Lynn, executive director of Americans United for Separation of Church and State. “It is vitally important that President Obama choose a high court nominee who understands that government may not meddle in matters of religion.”

In a strongly worded dissent in a 2002 ruling upholding an Ohio voucher program that benefited private religious schools, Stevens wrote: “Whenever we remove a brick from the wall that was designed to separate religion and government, we increase the risk of religious strife and weaken the foundations of our democracy.”

The Baptist Joint Committee for Religious Liberty praised Stevens as “a friend of church-state separation,” but criticized his siding with a 1990 ruling that allowed Oregon anti-drug laws to halt the use of peyote, a hallucinogenic drug, in Native American religious ceremonies.

J. Brent Walker, the committee’s executive director, said he hopes Obama will nominate a successor “who will be willing to permit — or even require — the government’s accommodation of religion in appropriate cases and to respect the autonomy rights of religion and religious organizations.”

Jay Sekulow, chief counsel of the American Center for Law and Justice, a conservative Christian law firm, called for a thorough confirmation process for Stevens’ successor, “with specific focus on the nominee’s judicial philosophy including how the nominee views the Constitution, the role of judges, and the rule of law.”