This action arises out of defendants’ representation of plaintiff in an action brought by plaintiffs landlord. During the course of said action, defendants drafted three tenders that purported to be made pursuant to CPLR 3219. This Court found that the tenders were conditional and therefore did not act to stop the accrual of interest on the landlord’s claim (Solow Mgt. Corp. v Tanger, 1 AD3d 165, 166 [2003]). In addition, in the underlying action, defendants filed untimely post-trial briefs, which were not considered by the court, and prepared, but did not file, an appellate reply brief, contrary to their written acknowledgment to plaintiff.
While we reject defendants’ argument that the tenders were proper, the finding that they were ineffective merely reflects an unsuccessful litigation strategy and does not constitute negligence. In order to be effective, a CPLR 3219 tender must be unconditional (see Castle Coal & Oil Co. v Frank's Fuel, 45 AD2d 836 [1974]), and defendants are collaterally estopped from contesting the determination that the tenders were conditional (see Buechel v Bain, 97 NY2d 295, 303 [2001], cert denied 535 US 1096 [2002]; Ryan v New York Tel. Co., 62 NY2d 494, 500 [1984]). In any event, by including a “reservation of rights” in the tender notice, defendants imposed a condition on the tender, by seeking to allow plaintiffs defenses and counterclaims to survive, contrary to a satisfaction of the landlord’s claim in that action (see CPLR 3219). Having chosen the litigation strategy of employing a CPLR 3219 tender, defendants were obligated to execute the strategy in compliance with the statute. This does not necessarily constitute malpractice in the context of the ongoing dispute between Solow and plaintiff which involved six separate and ongoing lawsuits arising out of a rent strike. An *287explication of this strategy necessarily requires trial as it is a contested issue unresolved by discovery. Concur-Nardelli, J.P., Williams, Sweeny and Catterson, JJ.