Shares in Abu Dhabi's Aldar Properties drop 6.1 percent to a two-week low, extending losses since announcing an all-share merger with Sorouh Real Estate.
Shares in Sorouh slip 1.8 percent, down from Monday's 25-month high.
Both stocks had more than doubled in price over the past year in anticipation of the state-backed merger, while the terms of the deal looked positive for Sorouh shareholders.
Sorouh shareholders will receive 1.288 Aldar shares for every share in Sorouh, which will be delisted once the merger, subject to shareholder approval, is completed, the companies said on Monday.
Abu Dhabi's index rises 0.1 percent to 2,782 points, as heavyweight Etisalat supports with a 1.2 percent gain.