Donald Trump. REUTERS/Kevin Kolczynski Real-estate mogul Donald Trump isn't happy with Pfizer and Allergan's announcement on Monday that the two companies would merge to form a corporate drug-making behemoth.

"The fact that Pfizer is leaving our country with a tremendous loss of jobs is disgusting," he said in a statement to Business Insider.

The Republican presidential front-runner added: "Our politicians should be ashamed."

The $160 billion merger would allow Pfizer to relocate its headquarters from the US to Ireland, where Allergan is incorporated and the corporate tax rate is much lower.

This is an example of a so-called corporate inversion, a hot-button issue on the 2016 campaign trail. Trump has been particularly critical of US companies that shift their operations oversees. For example, he has repeatedly vowed never to eat Oreo cookies again to protest Nabisco moving a plant to Mexico.

The two leading Democratic presidential contenders — US Sen. Bernie Sanders (I-Vermont) and former US Secretary of State Hillary Clinton — also blasted the Monday megamerger announcement.

"For too long, powerful corporations have exploited loopholes that allow them to hide earnings abroad to lower their taxes. Now Pfizer is trying to reduce its tax bill even further," Clinton said in a statement. "This proposed merger, and so-called inversions by other companies, will leave US taxpayers holding the bag."

Sanders said: "The Pfizer-Allergan merger would be a disaster for American consumers, who already pay the highest prices in the world for prescription drugs. It also would allow another major American corporation to hide its profits overseas."

Pfizer defended the merger as "a great deal for America."

"It allows us to continue to sustain an investment of approximately $9 billion mainly spent in the United States," Pfizer chief executive Ian Read said in an interview with Allergan CEO Brent Saunders and CNBC's Meg Tirrell after the announcement.

"We have 40,000 combined employees in the United States," he added. "So I think it's a great deal."