The US International Trade Commission has postponed by one day its planned vote on whether Bombardier's sale of CS100s to Delta Air Lines in 2016 caused harm to Boeing.
The four-member trade panel in Washington DC will now vote on the matter on 26 January at 14:30.
The ITC delayed the vote due to the US government's recent three-day shutdown, it says.
If the panel rules in Boeing's favour, CSeries will be subject to 292% import duties already established by the US Department of Commerce.
Those duties will disappear if the panel finds no harm.
Though the ITC is a six-commissioner body, it currently has only four sitting commissioners.
A tie by those commissioners equates to a finding that Bombardier's sale did harm Boeing, the ITC confirms.