It's closing in on D-day for AstraZeneca and Pfizer to commit to a merger deal. The pharmaceutical giants have until Monday, May 26 to agree upon terms. However, stakeholders of AstraZeneca are advising the smaller of the two to delay discussions to later in the year so as to push for a higher offer. According to The Financial Times, BlackRock (a major shareholder with an 8% stake) backed the company's recent rejection of Pfizer's $120 billion offer. Under U.K. M&A regulations, should the May 26 deadline come to pass with no deal, Pfizer would not be allowed to make another unsolicited deal for six months. AstraZeneca, however, could choose to reopen discussions after three.