There's more than one way to register as tax-exempt. A 501c(3) is strictly prohibited from political involvement. A 501c(4), on the other hand, can get involved in politics and even lobby. However, it must follow federal election law: It can't tell voters to vote for or against a candidate, and it can't run ads that mention a candidate within 30 days of a primary or 60 days of a general election, according to IRS and FEC code.

Craig Nelsen, president of ProjectUSA, said his group is within its nonprofit mission of reducing legal immigration to sustainable levels and ending illegal immigration.

"We don't raise money for candidates, we don't endorse candidates, we don't take sides on candidates," Nelsen said.

Cannon's agricultural jobs bill would grant temporary status to some illegal immigrants and give them a path to eventually earn permanent status.

Cannon has said the bill is not amnesty because of its limited scope and punitive measures such as a work requirement and fines.

The IRS sent letters to 501c(3)s in April warning them that political involvement could jeopardize their tax-exempt status and subject them to a possible excise tax on the amount of money spent on that activity.

"These organizations cannot endorse any candidates, make donations to their campaigns, engage in fund raising, distribute statements or become involved in any other activities that may be beneficial or detrimental to any candidate," the letter said.

Kirk Jowers, deputy general counsel for the Washington-based Campaign Legal Center, said of ProjectUSA: "This group is over the c(3) line. The Web site even says that it is targeting members who are vulnerable in the next election."

Tax attorney and state Sen. John Valentine, R-Orem, said by specifically targeting nine congressional districts, and grading lawmakers, "it would be pretty hard to say this is just education. . . . It is pretty close to the line."

The radio ads paid for by the Coalition for the Future American Worker say that Cannon's bill encourages "mass immigration" by providing amnesty for "about a million illegal foreign workers already here."

Dan Stein, executive director of the Federation for American Immigration Reform Congressional Task Force, a member of the coalition, said the ads targeted Cannon's policy.

Jowers said the coalition's ad may be "a little unfair" but is still a legal ad with a "firm issue."

Cannon alleges groups such as ProjectUSA and Coalition for the Future American Worker are connected to "anti-life" groups and people seeking "zero population, sterilization, abortion, eugenics and euthanasia."