President Obama has repeatedly said that if Congress won’t act on certain issues, then he would do so unilaterally—within the laws of the Constitution, of course. As he said in January, “I’ve got a pen and I’ve got a phone.”

So far, he has backed up those words. Obama has already announced one executive order that increases the minimum wage for workers under federal contracts and another that prohibits federal contractors from discriminating based on sexual orientation. In March, the president directed the Labor Department to revamp overtime rules. And his most controversial executive order is yet to come: In the fall, Obama is expected to announce that he will grant deferred status to possibly as many as five million undocumented immigrants.

On Wednesday, the president revealed yet another area where the administration is looking to act unilaterally: tax inversions. American companies use tax inversions to lower their tax bills by officially changing their tax jurisdiction to somewhere with a lower rate. They do so by merging with a foreign firm, but none of their operations change. Their management and control remain in the United States and Americans still make up the majority of their shareholders. All these companies have done is avoid U.S. taxes.

In 2014, many U.S. companies, particularly those in the pharmaceutical industry, have used an inversion to reduce their tax bills. This has set off a flurry of activity within the Democratic Party to stop this strategy. Treasury Secretary Jack Lew has called the practice unpatriotic. In fact, even some Senate Republicans, who have long argued that tax inversions should be addressed in comprehensive tax reform, have hinted at a willingness to pass a short-term fix. But in the GOP-controlled House there is little appetite for any such legislation, so Obama has decided to examine if he can deter these deals without Congressional help.

“We don’t want to see this trend grow,” Obama said at a news conference Wednesday. “We don’t want companies that up until now were playing by the rules looking over their shoulder at some competitor gaming the system … We want to move quickly—as quickly as possible.”