It is not unusual for members of Congress to arrange group rentals in Washington to share housing costs and, for some, underline their continuing “outsider” status. What is highly unusual, and unjustifiable, is the tax-exempt status as a religious institution enjoyed by a boarding house called the C Street Center that caters to conservative Christian lawmakers.

The $1.8 million townhouse came to public notice last year when three recent tenants  Senator John Ensign; Mark Sanford, the South Carolina governor and former congressman; and former Representative Charles Pickering Jr.  were embroiled in marital infidelity scandals. Mr. Pickering was accused by his estranged wife of entertaining a mistress at the house.

The center soon lost most of its city tax exemption, after District of Columbia officials decided it was a residence, not a church. And now a coalition of mainline Christian ministers is demanding that the Internal Revenue Service end the center’s federal tax exemption and its shield of nontransparency. The coalition is rightly concerned that the center is exploiting, and thereby cheapening, the constitutional protections guaranteed legitimate religious institutions.

The ministers say the center should be investigated as “an exclusive club for powerful officials” who reportedly enjoy low rents and other tax-subsidized benefits in a rooming house “masquerading as a church.”