Republican Sen. Ron Johnson's decision to block the judicial nomination of a University of Wisconsin law professor has drawn a pointed letter of protest by a group of legal academics from around the country.

Johnson has single-handedly held up consideration of Victoria Nourse for the 7th Circuit U.S. Court of Appeals, which reviews federal cases from Wisconsin, Illinois and Indiana.

"For a single senator from one state within the Circuit to assert a hold, months after the nomination was complete, undermines Wisconsin's merit-based selection system, blocking highly qualified nominees from a hearing and a vote," reads the letter to Senate Judiciary Chairman Patrick Leahy of Vermont and the panel's top Republican, Sen. Charles Grassley of Iowa. "The effect is an unbreakable one-person filibuster."

By tradition, the objections of even senators in the minority party to judicial nominees from their own state are given great deference. Leahy, a Democrat, won't move nominations under those circumstances.

But the professors said that Johnson is "retroactively" asserting his privilege to block a hearing, since the nomination by President Barack Obama pre-dates Johnson's election by half a year.

"Typically new senators have no power to countermand completed presidential nominations," the letter asserts.

Johnson contends the Nourse nomination effectively "expired" when she didn't get a hearing last year. Nourse was among many nominees whom the Senate failed to act on in the run-up to the 2010 midterm elections. The GOP freshman has taken the same position on another Obama nominee for the federal bench - former state Supreme Court Justice Louis Butler, whose confirmation has also stalled out.

While Johnson's public objections to Nourse have been largely procedural, he now says he opposes the nomination on its merits as well, saying she isn't well-known enough in the Wisconsin legal community to occupy one of the state's traditional slots on the 7th Circuit in Chicago.

"Victoria Nourse really has very little connection to the state of Wisconsin, and nobody in the legal community in Wisconsin knows anything about her," Johnson told the Journal Sentinel last month.

Nourse has been with the University of Wisconsin Law School since 1993. Before that she worked for the Senate Judiciary Committee under Joe Biden when the vice president served in the Senate from Delaware. Nourse also worked in the late '80s for the Senate committee that investigated the Iran-contra affair.

Wisconsin Sen. Herb Kohl defended the nomination, saying Monday, "I think she's well-qualified and deserves consideration."

Johnson is also asking for changes in the way the state's federal nominating commission works. It's a system Wisconsin senators have used for several decades to screen applicants for federal judge and prosecutor, and winnow them to a list of up to a half-dozen for the president to choose from.

"We're working as best we can to satisfy Senator Johnson that the commission is effective, impartial, that it has done well, that we should move forward with it," said Kohl in an interview.

Johnson said he is asking for changes in the makeup of the commission, whose structure depends on whether the state's senators belong to the same party as the president or not.

Right now when the two senators belong to different parties, the senator from the president's party appoints five members to the commission and the senator from the other party appoints three. (The remaining three to four slots on the commission are filled by the State Bar or by the state's two law schools, Marquette University and the University of Wisconsin).

In an interview Monday, Johnson said he wants "equal representation" on the commission - the same number of appointees to the commission as Kohl.

Johnson said that would have a "moderating influence" and "produce the best types of judges, not extremes from either side."