Updated, 10:30 a.m.:

Rep. Steve King (R-Iowa), one of the most outspoken GOP critics of the months-long push to overhaul the nation's immigration laws, launched what he said would be a six-hour press conference Wednesday morning to raise concerns about the pending legislation.

The Iowa lawmaker -- who earned the ire of the White House last week for a proposal that would require the deportation of the children of illegal immigrants -- began speaking around 9 a.m. in front of a crowd of about 300 on the East Lawn of the U.S. Capitol.

"I kind of like a microphone that has some volume to it," he shouted as he began.