Mundy said the proposal itself was flawed because it would give the governor disciplinary powers over the judiciary - powers that are now held by the state Supreme Court.
The technical grounds for the suit will be the allegation that the Department of State failed to meet advertising requirements as stipulated by law.
Mundy declined to name other plaintiffs, but an official of the Pennsylvania Conference of Teamsters said state Teamsters President John Morris would be among them.
The alliance of Morris and Mundy was unsettling to many advocates of the judicial discipline changes. While the two planned to file as individuals, the organizations with which they are closely tied are two of the state's most powerful interest groups.
Supporters of the judicial discipline changes reacted angrily to news of a suit.
"The notion that this is somehow about a constitutional argument of separation of powers is ridiculous," said Rep. Richard Hayden (D., Phila.), who helped guide the proposal through the legislature.
What is at stake, he said, is the current "consolidation of power" in the hands of the State Supreme Court. "The Supreme Court wants to control all disciplinary matters about members of the bench."
Norton Brainard, Morris' attorney, said organized labor and the Trial Lawyers Association had joined previously on issues, including recent opposition to legislation proposing limits on large damage awards in liability suits.
Brainard said that Morris had always opposed changes in the judicial system, and that he viewed the discipline amendment as a "prelude" to replacing the elections of judges with an appointment system, so-called merit selection, which unions strongly oppose.
In his suit, Mundy said he would allege that the state, in advertising the proposed changes, took "shortcuts" that had the effect of not making prospective voters aware of the major changes being considered.
Those changes, which involve replacing the current disciplinary system dominated by judges with a new, lay-dominated system, would give the governor control over judicial discipline through the appointment process, he said.
Mundy said his group supported recommendations for judicial discipline by the so-called Beck commission, which would have provided for more input into the system by the state Supreme Court.
Mundy said he opposed the measure's provision dealing with court funding, saying the language was an attempt by the legislature to overturn a state Supreme Court decision ordering the state to fund local courts.
He said comments on the House and Senate floor by legislative leaders that the intention of the language was not to reverse the order were "totally irrelevant" under law.
The proposed changes in the disciplining process and the funding language are scheduled to appear as two separate ballot questions.
Mundy said he was filing on behalf of himself, not the trial lawyers, but he noted that the trial lawyers recently passed a resolution opposing the proposed constitutional amendment.
Mundy said he would have preferred to act earlier, when the General Assembly was in the process of approving the proposed changes, but he said he must "plead guilty" for not having followed the legislation.
While the plan by Mundy and Morris to file suit was viewed by court-reform advocates as their most threatening challenge, another lawsuit against a portion of the proposal was filed yesterday.
Philadelphia lawyer Henry T. Reath, who was a member of the Beck
commission, filed a challenge to the question dealing with court funding, saying the "ambiguous language" of the amendment would "spawn . . . endless litigation" and destroy court-reform attempts. The Beck commission, formally known as Gov. Casey's Judicial Reform Commission, was chaired by Superior Court Judge Phyllis W. Beck.
Earlier this month, Philadelphia Common Pleas Court Judge I. Raymond Kremer filed suit to block the constitutional amendment from appearing on the ballot, citing many of the same reasons as Mundy.
Commonwealth Court has scheduled a hearing on Kremer's suit for Monday, and lawyers expect the other suits to be added to it. The Department of State has said it has "complied with all legal and statutory mandates as well as case law" in advertising the proposal.