With the Internal Revenue Service reeling after revealing it intentionally targeted conservative groups seeking tax-exempt status, U.S. Rep. Keith Ellison says the agency and Congress should "get more engaged, not less" on campaign finance.

Targeting groups based on their politics is wrong; all groups, liberal and conservative, should be scrutinized, Ellison said Monday during an appearance on MSNBC's "All In with Chris Hayes."

The IRS has often failed to draw lines of distinction between "social welfare" non-profits and political groups, he said.

"We need Congress to act to say that we're going to scrutinize all groups that are electioneering when they really should be doing social welfare," Ellison said. "The thing I fear ... is that the IRS will be backed off. The IRS should get more engaged, not less ... We need to redouble our efforts to bring real campaign finance forward."

On Friday, the IRS apologized for singling out conservative and tea party groups for extra scrutiny during the 2012 election cycle, originally blaming the problem on low-level functionaries in their Cincinnati office. The scandal has now ensnared the former and acting directors, who repeatedly denied the targeting.

Reform groups and some congressional Democrats, Ellison among them, have urged the IRS to investigate the tax-exempt social welfare organizations that reel in hundreds of millions of dollars in anonymous donations. The groups spent at least a quarter of a billion dollars on political activities during the last election cycle, according to the Washington, D.C.-based Center for Responsive Politics.

Reform supporters now fear that the IRS will cave and abdicate its oversight role, allowing all the organizations to go unchecked.

"There are clearly flagrant misuses of the term social welfare," Ellison said. "This needs to be reined in. Congress should move forward to do it, on a fair basis, not back off."