Updated: May 31, 11 a.m.

As the Senate prepares to take up sweeping and controversial immigration reform legislation next month, NumbersUSA is hitting the airwaves to oppose the legislation in 18 states.

The president of NumbersUSA, former journalist Roy Beck, would not disclose the exact amount of the buy but said it is in the hundreds of thousands of dollars. The ads, running on both radio and TV, began airing over the holiday weekend and are scheduled to run through May 31, mostly on news programs. Congress is in recess this week so many senators are back in their home states where the ads are airing. Beck said he hopes to raise enough money to keep the ads on the air through the Senate debate and vote on the immigration bill.

Though the ads do not mention lawmakers by name, they are running in states that are home to senators who are considered to be swing votes, including Orrin Hatch, R-Utah, Rob Portman, R-Ohio, Rand Paul, R-Ky. and Jerry Moran, R-Kansas. The tech lobby is pushing those same senators to support the immigration legislation, which would increase the number of visas for high-skilled workers. NumbersUSA is opposed to the increase in visas.

NumbersUSA, which formed in the late 1990s and employs lobbyists, operates both a 501(c)3 and a 501(c)4. The current batch of ads is paid for by the 501(c)3, Beck said, but both arms underwrite ads depending on their lawyers' advice, he said. The group ran ads earlier this year targeting Sen. Lindsey Graham, R-S.C., and Mark Begich, D-Alaska, for supporting immigration reform. Neither group is required to report the ads to the Federal Election Commission, but Sunlight has created two tools that can track otherwise under-the-radar issue advertising, Political Ad Sleuth and Ad Hawk.

While the total of the latest Numbers buy isn't known, Federal Communications Commission records, available online for the nation's top 50 TV markets, suggest that it is substantial. In Pittsburgh, NumbersUSA buys on two stations total more than $35,000. In the Salt Lake City market, buys on TV stations KSL and on station KUTV totalled almost $48,000.

The TV ad, seen above, criticizes the immigration bill for inviting more foreign workers into the country while Americans need jobs. Its claim of 33 million in "new work permits to foreign job seekers" represents the number of people who would be granted papers to work legally in the United States over the course of a decade and is based on estimates by NumbersUSA.

The number is disputed by the pro-immigration reform group America's Voice. It pointed to a report by the liberal Center for American Progress that says that the bill would lower immigration levels because of decreased numbers of illegal immigrants entering the country. America's Voice deputy director Lynn Tramonte said that "NumbersUSA is against immigration, period. Of course they're going to try to trump up numbers to try to scare senators and congressmen into voting against immigration reform."

Unlike other opponents of the immigration bill, Beck said his group is not focusing on the so-called amnesty the bill would provide to an estimated 11 million people now living in the country illegally. Beck believes the bigger concern is the increase in legal immigration the bill would allow. He is more focused on the 11 million new legal immigrants he believes the bill will produce over the next decade. NumbersUSA wants to more than halve that figure. "We are trying to reduce the 11 million a decade down to about 5 million a decade," he said.

The TV ads are running in Idaho, Indiana, Kansas, Kentucky, Missouri, Nevada, North Carolina, North Dakota, Ohio, Pennsylvania, Utah and West Virginia. Radio ads are running in Idaho, Indiana, Kansas, Kentucky, Mississippi, Nebraska, North Dakota, Nevada, Tennessee, and Wyoming.

Correction, May 31, 11 a.m.: This post has been updated to correct a mistake made by NumbersUSA. The number of immigrants that NumbersUSA says will enter the U.S. in the next decade is in fact based on its own research, not an outside study.