Multinational private companies that are headquartered in Abu Dhabi, such as Citibank, are subject to the Federal Pension Law, i.e., they should be registered with GPSSA as well as their other branches across the UAE (including those in Abu Dhabi).
Local entities that are headquartered in Abu Dhabi and that have branches all over UAE are subject to the Abu Dhabi Pension Law (e.g. First Abu Dhabi Bank).