Pfizer has decided to walk away from its planned $150 billion combination with Allergan, after the Obama administration took aim at a deal that would have moved the biggest drug company in the US to Ireland in order to lower its taxes, according to people familiar with the matter.

The companies are expected to announce the deal’s termination as early as Wednesday morning, after Pfizer’s board voted Tuesday to halt the combination and the New York-based drug company notified Allergan, WSJ reports.

Pfizer will pay Allergan a small break-up fee, the people said. The merger agreement called for a fee covering Allergan’s integration-planning expenses of up to $400 million in the event that tax rule-changes rendered the deal unworkable.

By combining with Ireland-based Allergan, Pfizer could not only cut its tax rate but also get access to the billions of dollars in revenue it was keeping overseas in order to avoid paying US taxes on top of the taxes it had already paid in foreign countries. There were non-tax benefits, too.

The White House, meanwhile, denied the announcement of new rules about inversions was targeted at a specific company.

“The Treasury Department is not focused on a specific transaction, it’s focused on specific loopholes,” White House press secretary Josh Earnest said.