Tax inversion target companies hit by U.S. crackdown by Laura Lorenzetti @FortuneMagazine September 23, 2014, 10:22 AM EDT E-mail Tweet Facebook Google Plus Linkedin Share icons Companies that were targets for tax inversion deals by U.S. companies have taken a dive in the stock market Tuesday after the White House announced sweeping efforts to crack don on tax inversions. Tax inversions, where a U.S. company buys a foreign rival in order to move its headquarters and tax base abroad, have been all the rage this year. Thirteen inversion tax-inversion deals worth $178 billion have been announced since January, according to Dealogic. European drug makers have been a prime target for these inversion deals, and stocks of the target companies were hit particularly hard Tuesday morning as investors worried about the status of potential takeovers. Names under the cosh include AstraZeneca AZN , the UK-based pharmaceutical company pursued by Pfizer PFE . U.K.-based Shire also declined. It agreed to be bought by AbbVie ABBV in July. Medical maker Smith & Nephew SNN , which has been a potential target for Kalamazoo, Mich.-based Stryker SYK , fell sharply too. Other rumored pharma takeover targets, such as Swiss drugmaker Actelion, have also seen their stock prices suffer. The Obama administration has been critical of companies fleeing America’s 35% corporate tax rate, and finally announced steps to rein in the practice. The U.S. Treasury Department will require U.S. companies to own less than 80% of a newly purchased entity, making it more difficult to invert. It also eliminated certain tax-free access to foreign units’ deferred earnings. The Treasury’s rules are immediately effective, but they will not be retroactive. Inversion deals that have already been completed will be unaffected.