The current member of parliament and former industry minister, 73, is said to be one of the more hardline members of the Union Solidarity and Development Party founded by former military leader General Than Shwe and now led by President U Thein Sein.
The US Treasury sanctions freeze any US-based assets he might have and ban Americans from doing business with him.
But the US stressed the sanctions apply to U Aung Thaung alone, and not to any government organisation with which he is associated.
"U Aung Thaung is actively attempting to undermine recent economic and political reforms in Burma and has been implicated in previous attacks on Burma's democratic opposition," the Treasury said.
"As the United States continues to support and monitor Burma's reforms, including democratic reform and the national peace process, we remain concerned that certain individuals have been working to counter these efforts."
The move comes as Myanmar's parliament agreed to consider changing the country's constitution to allow opposition leader Daw Aung San Suu Kyi to run for the presidency next year.
The current charter bars her from being president, yet her National League for Democracy party are expected by many commentators to dominate the polls in 2015.
The NLD has focused on altering a provision in the constitution that ensures the military in the former junta-ruled nation has a veto on any amendment to the charter.
It believes revising the clause will open the way for further changes to other constitutional provisions, including the ring-fenced proportion of soldiers in parliament and the effective bar on Daw Aung San Suu Kyi becoming president.
Daw Aung San Suu Kyi is currently ineligible because of a clause in the 2008 charter blocking anyone whose spouse or children are overseas citizens from leading the country. The Nobel peace laureate's late husband was British, as are her two sons.
The White House said on October 30 that US President Barack Obama spoke to U Thein Sein and Daw Aung SanSuu Kyi about next year's elections.
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