Fears of counterfeit $50 and $100 bills have disrupted foreign-exchange trade at Istanbul’s Grand Bazaar, the nation’s largest currency trading gray market.

According to the state-run Anadolu Agency, some bureaus at the bazaar, a hub for currency trading, stopped purchasing the bills, saying the counting machines they use can’t identify the fake notes.

“The number of counterfeit dollars isn’t clear,” Anadolu cited Resat Yilmaz, a tradesman at the Bazaar, as saying. “These bills have to be collected, which can take two weeks.” Money-counting machines also have to be updated, he added.

A representative for currency traders said the disruption has no basis and “there’s no fake currency” in circulation. He blamed banks for what he said was a “clogging” of trading.

“Banks should accept old dollar bills. Currently, no bank is doing that,” Mehti Seren, head of the Association of All Authorized Institutions and Foreign Exchange Offices, said in a press conference. “Clients are then returning the dollars to us. That’s what’s clogging the system.”