President Obama's second nominee to head the Transportation Security Administration signaled Wednesday that he would support unionization of the nation's 40,000 airport screeners.

Treading lightly on a topic that helped to derail the president's first nominee, Robert Harding acknowledged under questioning that the Obama administration wants the work force to have collective bargaining rights and said his job as TSA administrator would be to implement the change in a way that does not hurt security.

Harding's responses were careful and measured, even under questioning by Sen. Joseph Lieberman, chairman of the Senate Homeland Security Committee, who said he supports collective bargaining.

When several questions failed to elicit a direct response on the issue, Lieberman, a Connecticut independent, asked Harding whether "essentially what you're saying" is that he would give the president guidance on "how best to implement" the decision to unionize the work force. Harding responded, "Yes, Mr. Chairman, and make a recommendation to [Department of Homeland Security Secretary Janet Napolitano] and the president."

The unionization issue has been a flashpoint between some Democrats and Republicans. Sen. James DeMint, R-South Carolina, put a hold on the first nominee, Erroll Southers, after Southers declined to say whether he supported unionization of screeners. Southers eventually withdrew his name from consideration after another controversy erupted involving a decades-old personnel matter.