Howard Ganz, an MLB lawyer, said in a letter to U.S. District Judge Edgardo Ramos that Rodriguez's claims do not come "remotely close" to what is needed to overturn an arbitration decision in federal court.
Ganz's letter, dated Monday and filed Tuesday, said the lawsuit should be tossed because a court is not empowered to re-examine the merits of an arbitration decision.
Ganz said in the letter that the standard for vacating an arbitration award "is purposefully high and specifically designed to prevent courts from substituting their own judgment for that of the labor arbitrators selected by the parties."
"A court must confirm an award even when the arbitrator has offered only a barely colorable justification for the outcome reached, and even if the court considers the arbitrator's interpretation of the contract to be plainly wrong," he wrote.
Rodriguez's claims in his lawsuit were considered by the arbitrator and resolved based on evidence and arguments, along with the arbitrator's interpretation of collectively bargained agreements, Ganz said.
He also noted that Rodriguez did not deny engaging in the misconduct that was alleged during the arbitrator's hearing or in his lawsuit.
Ramos set Feb. 14 for a conference and directed lawyers for Rodriguez to respond to the league's claims in a letter of their own by Feb. 7.
MLB suspended the three-time AL MVP for 211 games last August, and the players' union filed a grievance. Arbitrator Fredric Horowitz on Jan. 11 cut the suspension to 162 games and the 2014 postseason, concluding Rodriguez used banned substances each year from 2010-12 and twice tried to obstruct MLB's investigation.
Rodriguez did not testify in the grievance proceeding, walking out after Horowitz refused to order Commissioner Bud Selig to testify.
Rodriguez sued MLB and the Major League Baseball Players Association on Jan. 13 to overturn the decision. He accused the league of engaging in "ethically challenged behavior" and leaking information to the media in violation of baseball's confidentiality rules. He also accused Horowitz of acting "with evident partiality."
His lawsuit accused the players union of "bad faith," saying its representation during the hearing was "perfunctory at best."
In a footnote, Ganz wrote that the players' union plans to seek dismissal of the claim that it breached its duty of fair representation and said the league will join in that application to the court.
Lawyers for Rodriguez and the players union did not immediately respond to a message seeking comment.