The bishops of America's 196 Catholic dioceses and archdioceses - planning to tackle the child sex abuse crisis and stop further crimes - have been ordered by Pope Francis not to vote on any of their proposals.
He does not want their gathering in Baltimore to address bishops' accountability on sexual abuse until he leads a worldwide meeting in February of church leaders.
His request was delivered by the president of the US Conference of Catholic Bishops, Cardinal Daniel DiNardo, yesterday in the opening minutes of the meeting.
"At the insistence of the Holy See, we will not be voting on the two action items," DiNardo said. He said he was "disappointed" by the pope's directive.
Anne Barrett Doyle, co-director of BishopAccountability.org, called the last-minute order from the Vatican "truly incredible".
"What we see here is the Vatican again trying to suppress even modest progress by the US bishops," said Ms Doyle, whose group compiles data on clergy abuse in the Church.
"We're seeing where the problem lies, which is with the Vatican. The outcome of this meeting, at best, was going to be tepid and ineffectual, but it's actually going to be completely without substance."
Archbishop Christophe Pierre - the Vatican's ambassador to the US - defended what bishops have already done to reduce instances of clergy abusing children and expressed hesitancy about anyone other than clergy - such as lay leaders or civil authorities - punishing abuse.