A top Democrat warned on Tuesday a recent string of so-called tax inversions could foreshadow future moves as U.S. firms look to dodge American taxes.

Ron Wyden, the chairman of the Senate finance committee, said "up to 25 more companies" are considering deals that would shift their headquarters to tax havens abroad, according to the Financial Times.

The move comes after America-based AbbVie (ABBV) inked a $54 billion deal to acquire Irish drugmaker Shire (SHPG). Medtronic (MDT) and Covidien (COV) unveiled a similar tie-up in June.

Read: Will Congress Scuttle the AbbVie-Shire Merger?

Meanwhile, blue-chip pharmaceutical player Pfizer (PFE) attempted to scoop up rival AstraZeneca (AZN), in a pact that would have created the world’s biggest biotech company.

The U.S. has a federal corporate tax rate of 35%, while the U.K.’s main corporate rate is 21%.

Click here to read the full story on FT.com.