The measure aims to establish a common international framework for enforcing intellectual property rights.
“Protecting intellectual property is essential to American jobs in innovative and creative industries," U.S. Trade Representative Ron Kirk said in a statement after signing the agreement. "The ACTA provides a platform for the Obama Administration to work cooperatively with other governments to advance the fight against counterfeiting and piracy."
But Issa called the measure an "unconstitutional power grab begun by the Executive Branch to bypass Congress' Constitutional authority over international commerce and intellectual property rights protections."
Issa was one of the leading opponents of two bills to crack down on online copyright infringement, the Stop Online Piracy Act (SOPA) and the Protect IP Act (PIPA).
Congressional leaders were forced to pull the bills after a massive Web protest sparked an explosion of voter anger. Critics said the legislation would stifle innovation and restrict free speech.
The Obama administration expressed concern over the bills in January, warning Congress not to "undermine" the Internet.
"ACTA represents as great a threat to an open Internet as SOPA and PIPA and was drafted with even less transparency and input from digital citizens," Issa said. "This agreement was negotiated in secret and many of its vague provisions would clearly increase economic uncertainty, while imposing onerous new regulations on job creators, Internet service providers, innovators and individual Americans."
The European Union's top court is currently reviewing whether the trade agreement violates free speech protections.