The recent reports claiming that two big pharmaceutical companies, Pfizer and Allergan, are currently in talks of uniting has been confirmed. New reports say that the two healthcare giants might be announcing one of the biggest healthcare mergers on Monday.

Pfizer has been in the headlines recently when the company has been reportedly eyeing to purchase Allergan, an Ireland-based healthcare company, for $150 billion. The Globe and Mail reports that Pfizer's board are in their final stages to secure approval today and finally make an official offer to Allergan.

The deal comes after Pfizer paid 11.3 of its shares for each Allergan share, including a small cash component which amounts to less than 10 percent of the value of the deal. However, official statements from the two companies have yet to be released.

Furthermore, what is head-turning with the current speculations is that the deal will make Pfizer move from its original U.S.-based operations to Ireland, where Allergan is currently situated. Not only that, speculations rose when just recently, the U.S. Treasury pointed out the issue on inversion.

According to The Guardian, Pfizer and Allergan's deal, which will be the largest medical healthcare merger in history, will have an advantage in cutting its tax range from the current 15 percent to 39 percent in the U.S. to only 12.5 percent.

Inversion is when companies relocate to foreign countries for a more favorable tax environment, making it look like it was bought by smaller companies like Allergan, when, in fact, the bigger company will have most of its shares like Pfizer.

And since Pfizer's Chief Executive Ian Read, 62, will be CEO of the combined company, and Allergan's current CEO Brenton Saunders, 45, will be Read's deputy, The Guardian speculates that the merger can be considered as an inversion.

"US companies are currently taking advantage of an environment that allows them to move their tax residence overseas to avoid paying taxes in the US, without making significant changes in the nature of their overall operations," U.S. Treasury Secretary Jack Lew said as quoted by CNBC.

Despite the obvious moves of U.S. companies including Pfizer for tax avoidance according to The Guardian, the U.S. Government remains to be still and are just waiting for new legislation to come up to finally make restrictions from all the inversions happening.

"While we intend to take additional action in the coming months, there is only so much the Treasury Department can do to prevent these tax-avoidance transactions," Lew continued. "Only legislation can decisively stop inversions," he said as quoted by CNBC.