Collectors of antiquities say they are finding it increasingly difficult to donate or sell items as museums move to curb the trade in looted treasures, according to The New York Times.

Institutions are demanding far more documentation than in the past on the histories of donated artifacts, seeking to establish ownership trails going back further than 1970 under guidelines laid down by the Association of Art Museum Directors.

The rules, drawn up on 2008, have been cheered by countries seeking to recover ancient cultural treasures, and by archeologists. But collectors say the shift has left them stuck with Classical objects they purchased in good faith from reputable sellers that no longer pass muster at museums, and they contend the institutions and scholarship will suffer as a result.