During his term, he drafted a new charter for the commission requiring a supermajority for any tax increase. Allentown voters approved the charter on April 23, 1996. In 1998, Toomey ran for the Pennsylvania's 15th congressional district, based in the Lehigh Valley region, after Democratic incumbent U.S. Representative Paul McHale decided to retire. Toomey won the six-candidate Republican primary with 27% of the vote. In the general election, Toomey faced Roy C. Afflerbach, State Senator and former state representative. During the campaign, Toomey criticized the agenda of the Clinton-Gore administration, especially its plans to modify the Internal Revenue Service. He said the plan did not "address the real fundamental problems plaguing American taxpayers" and said the IRS should be abolished. Later in the campaign, Toomey and Afflerbach debated the effectiveness of a flat tax-based system, an issue on which they sharply disagreed. Toomey promised to serve no more than three terms if elected. He defeated Afflerbach, 55%–45%. Toomey was reelected to a second term, defeating Ed O'Brien, president of the Bethlehem-based United Steelworkers Local 2598, 53%–47%. He won Lehigh County with 54% and Northampton with 51%. Toomey was reelected to a third term, defeating O'Brien again, 57%–43%. He won Lehigh with 58% and Northampton with 54%. In accordance with his 1998 pledge not to serve more than three terms in the House, Toomey did not run for reelection in 2004. He decided to challenge incumbent Republican U.S. Senator Arlen Specter in the primary instead. Toomey served as the U.S. Representative for from 1999 to 2005. In the House, he distinguished himself as a fiscal expert. He pushed to decrease government spending and to set aside money for debt reduction. In 2001, Toomey proposed a budget that would cut taxes worth $2.2 trillion over ten years, exceeding Bush's $1.6 trillion plan. In 2002, Toomey voted in favor of the Iraq Resolution, which authorized military action against Iraq. Toomey strongly opposed Bush's plan for illegal immigration, saying "I think it's a slap in the face for the millions of people throughout the world who decide to take the effort to legally enter our country." He was a longtime supporter of creating Medicare Part D, but said he would not vote for it unless it lowered costs and guaranteed competition between government and private insurers.