Turkey may cut logistic support to US troops in Iraq if the US Congress backs a bill branding the 1915 massacres of Armenians by Ottoman Turks as genocide.
The Foreign Affairs Committee of the US Congress is expected to approve a bill on the genocide issue.
Speaker Nancy Pelosi, a known supporter of the Armenian cause, could then decide to bring it to the House floor for a vote.
Turkey strongly denies Armenian claims, backed by many Western historians and a number of foreign parliaments, that up to 1.5 million ethnic Armenians suffered genocide at Turkish hands during World War I.
It says many Muslim Turks as well as Christian Armenians died in inter-ethnic conflict as the Ottoman Empire collapsed.
AK Party deputy leader Egemen Bagis said that if the bill is accepted, Turkey 'will be obliged to do many things we do not want to do'.
He cited the US dependence on Turkey for a large part of its logistical support in Iraq. Mr Bagis said Turkey would be obliged to cut this support.
Mr Bagis was speaking in a personal capacity, but Turkey's government has many times urged foreign countries, including the US, not to pass such resolutions, saying historians, not politicians, should judge historic events.
Last year, Turkey froze military and some commercial co-operation with France after the French National Assembly backed a bill that would make it a crime to deny the Armenian genocide, although the bill never became law.
US forces in both Iraq and Afghanistan get many of their supplies via the Incirlik military base in southern Turkey.
Mr Bagis said the bill might please Armenian-Americans for a few days but it would definitely have a long-lasting negative effect on the relationship between two strategic allies.
He left for Washington with two other Turkish lawmakers on to lobby Congress to drop the bill.
The Bush administration is opposed to the bill but Congress is now dominated by the Democrats.