A top House Democrat is taking legal steps to force the names of political donors to be disclosed.

Maryland Rep. Chris Van Hollen filed a lawsuit against the Federal Election Commission Thursday, challenging a regulation allowing independent groups spending money on political campaigns to shield the identities of their donors.

Van Hollen's lawsuit was filed in federal district court in Washington.

Since a Supreme Court ruling last year cleared the way for corporations and independent groups to spend freely on campaign activity, many have done so using money from anonymous donors.

Van Hollen said that practice violated an existing law requiring donor disclosure.