Speculation is hotting up that Pfizer will announce in a matter of days its intention to buy Dublin, Ireland-based Allergan for $150 billion, in what could be the pharmaceutical industry’s biggest-ever transaction.

According to Bloomberg, which cited “people familiar with the matter”, the groups are in “advanced talks” over a deal that would see the drug giant pay up to $380 a share for the Botox-maker.

A deal could be announced as early as November 23, the sources say, but also note that a final agreement may be delayed if the US Treasury Department steps in with any demands under tightening tax inversion laws, given that the move could see Pfizer relocate its HQ to Ireland to save billions of dollars from a lower corporation tax rate in the country.

The proposed marriage would create the world’s largest drugmaker with a market capitalisation in excess of $300 billion, exceeding Johnson & Johnson, currently valued at $277 billion, and annual sales approaching $53 billion.

Last year, Pfizer attempted a $118-billion takeover of UK-based AstraZeneca, only withdrawing in the face of staunch opposition from the AZ’ management, British politicians and media. Given that Allergan largely operates out of New Jersey in the US despite being headquartered in Ireland, the move may not receive as much opposition.