A spokesman for Sen. Mark WarnerMark WarnerOvernight Cybersecurity: Obama faces new scrutiny for Russia response | UK parliament cyberattacked | Election hacking fears put heat on DHS | Feds appeal to Supreme Court over data warrants Election hacking fears turn heat on Homeland Security Are Democrats trying to pin the blame for their own sins on Russia? MORE (D-Va.) said Wednesday it is "premature" to say whether the freshman senator will support the Employee Free Choice Act (EFCA).

"No one knows what the bill may look like when it gets to the floor, so the cloture question is premature," Warner spokesman Kevin Hall told The Plum Line's Greg Sargent.

Warner had written constituents in late March saying he believed "EFCA should be debated and voted upon by the Senate," lending supporters of the bill in the organized labor movement the impression that the centrist Democrat would at least support ending debate on the legislation.

Supporters of EFCA (or "card check") have experienced some setbacks in their effort to push the organizing bill through the Senate. In recent weeks, Sens. Arlen Specter (R-Pa.) and Blanche Lincoln (D-Ark.) have backed off from supporting the bill in its present form, and other Senate lawmakers have wavered on their support for the legislation.