Happily we don't see these very often.
John Allen spoke generally in another case about this penalty: Dismissal from the clerical state ex officio et in poenam, meaning an involuntary laicization approved personally by the pope. This is a rare option because it short-circuits procedural guarantees. In most cases, however, the accused priest has already had several opportunities to mount a defense. Sometimes he may already have been convicted criminally. [Note: this six year old statement applied to a priest. Shanahan was a deacon. I'm no canon law expert, but I would assume the procedure applies to all clerics and a deacon is an ordained cleric.]
On June 26, 2009, the Supreme Pontiff, Pope Benedict XVI, decreed that Deacon Martin Kelly Shanahan, a permanent deacon of the Archdiocese of Saint Paul and Minneapolis, is dismissed from the clerical state ex officio et in poenam and released from all obligations of the clerical state. This supreme penalty was imposed on Mr. Shanahan after he abandoned the Catholic Church, sought 'priestly ordination' from a female bishop of the Apostolic Catholic Orthodox Church, and then attempted to administer the sacraments (simulation). The same decree indicated that the canonical censures incurred by Mr. Shanahan as a result of his schism remain in force.
The Archdiocese wishes the faithful to be aware that any ‘Mass’ or sacrament administered by Mr. Shanahan, with the exception of baptism, is invalid. The August 2000 declaration by the Congregation for the Doctrine of the Faith, Dominus Iesus, does not apply to Mr. Shanahan’s attempted presbyteral ordination nor does it make any statement regarding the validity of the Orders of the Apostolic Catholic Orthodox Church.
Thanks to Michael for pointing out the need for the clarification.