"We, Turkish Americans, cannot find the words to express our shock and deep disappointment when we hear that the U.S. might be helping a terrorist organization in Syria which is an offshoot of the PKK," according to a letter signed by leaders of the Turkish American National Steering Committee, an umbrella organization of 150 Turkish American organizations.
The letter published in the Washington Post newspaper noted that as a branch of the PKK -- listed as a terrorist group by Turkey, EU and the U.S. -- the PYD "targets the national security, territorial integrity, and people of a country which is one of the strongest allies the United States has in the region".
U.S. officials have said a coalition assembled to fight Daesh has provided air support to the PYD but media reports claim the U.S. has also provided 50 tons of ammunition to the militant group.
The Pentagon has insisted that the supplies were sent to a Syrian Arab Coalition and that the U.S. does not give arms to the PYD.
The PKK is responsible for terrorist attacts that has claimed the lives of an estimated 40,000 Turkish citizens during the past 30 years.
After years of relative calm, the conflict with the PKK resumed earlier this year. The group has conducted surprise attacks in Turkey that has killing more than 150 victims since July.
Citing a twin suicide bombing in Ankara last month that killed at least 102 victims, the letter said Turkey became a Daesh target because of its contribution to the U.S.-led coalition targeting the militant group in Syria and Iraq.
Turkish jets have targeted Daesh and Turkey opened its bases to coalition aircraft to conduct operations in Syria and Iraq.
The letter also urged Obama to help Turkey deal with regional crises, particularly with an influx of Syrian refugees.
"Turkey is once again confronted with daunting challenges as this time the countries in its neighborhood are failing and the region is dragged into the scourge of terror and ruthless war," the letter read. "As our president and friend of Turkey we urge you to assist Turkey in this immense endeavor of preserving the lives and the dignity of millions of Syrians, Iraqis, Afghans and others."
Turkey has opened its borders to provide a safe haven for more than 2.5 million refugees since the civil war began in Syria in 2011.
The country is also hosting hundreds of thousands of refugees from other countries.