Senior House Democrat Sues I.R.S. Over Tax Exemptions Representative Chris Van Hollen filed suit in Federal District Court on Wednesday to force the Internal Revenue Service to block tax-exempt "social welfare" organizations from engaging in any overt political activity. The suit, joined by the campaign watchdog groups Democracy 21, Public Citizen and the Campaign Legal Center, signaled that forces for increased campaign finance regulation may be regaining their footing after the controversy over the I.R.S."s targeting of political groups had put them on the defensive for months. But the battleground appears to be shifting from Congress to the courts. For decades, the I.R.S. has struggled with defining the meaning of "social welfare" when determining whether a group should be eligible for tax-exempt 501 (c) (4) status. The government has generally said a group's "primary" purpose should be social welfare, allowing a significant amount of its work - roughly 49 percent - to be partisan politics. And those groups do not have to publicly disclose their donors. With the Supreme Court's deregulation of campaign finance laws, the issue has become more controversial. In 2012, 501 (c) (4) groups pumped $256 million into the presidential campaign cycle, triple the amount spent in the 2008 cycle and 33 times the $7.6 million they spent in 2004. The lawsuit, filed in the United States District Court for the District of Columbia and citing the tax law that created such tax exemptions, says the I.R.S. should rule that the exemptions should go only to groups exclusively engaged in social welfare work. That would prohibit any tax-exempt activity aimed at electing or defeating specific political candidates. Many Democrats have sought legislative remedies to force more disclosure amid the flood of money to outside political groups. But the scandal over the I.R.S."s targeting of political groups - conservative and liberal - for extra scrutiny has diminished the already low prospects of any such legislation. Advocates of the lawsuit said the case law was clear. Congress never intended a 501 (c) (4) to be buying attack ads aimed at candidates. And they said Republicans should back the effort if they really believe the I.R.S. should not be trying to determine the lawful balance between "social welfare" and political activities. "If you agree the I.R.S. should not be in the business of looking into the activity of every organization to determine how much is political versus social welfare, then you should welcome this," said Mr. Van Hollen, a senior House Democrat from Maryland. By and large, Republicans have reached a similar conclusion but with an opposite remedy. The I.R.S., they say, should simply leave the groups alone and not infringe on their activities at all.