After the earlier silence of the unions about DISCLOSE, this statement from Richard Trumka of the AFL-CIO could mark a turn toward it:

Congressional leaders today took a vitally important first step to begin to address the Supreme Court’s recent decision in Citizens United v. Federal Election Commission. The AFL-CIO commends these efforts and supports increasing disclosure and reexamining some current campaign finance rules.
The Court’s decision threatens to widen the gulf between corporate power and that of ordinary people, unions and other membership and civic groups. It is imperative that legislation counter the excessive and disproportionate influence by business. We must not allow corporations to hijack the democratic election process from the American people.
America deserves a system of campaign finance regulation that promotes democratic participation in elections by individuals and their associations; protects free and independent political speech; offers public financing to candidates while firmly regulating contributions to them; and guarantees effective disclosure of who is paying for what.
We will carefully review this complex legislation and fully participate in the legislative process by working with allies and both Houses of Congress to produce a final bill that reflects these principles and advances these goals.