By Nektaria Stamouli

ATHENS--Greek retailers and small businesses are starting to see select items disappear from store shelves as a widening credit squeeze weighs on importers, but industry officials expect that the real crunch will become more evident by September if uncertainty remains regarding the country's future in the euro zone.

Last week two of the world's biggest providers of trade credit, Germany's Allianz SE (ALV.XE) unit Euler Hermes (ELE.FR) and France's Coface, said they won't offer new insurance cover for exporters shipping goods to Greece as they find it increasingly difficult to price such cover amid worries that the country may quit the euro zone.

Credit export insurance ensures that exporters are paid if their client defaults. The loss of such cover is likely to have a major impact on the willingness of companies to trade with Greece, particularly given the country's deteriorating economy.

"We are close to what happened at the time of the break up in the former Soviet Union back in the 1990s," said Dimitris Asimakopoulos, chairman of the Hellenic Confederation of Professionals, Craftsmen and Merchants.

Back then, Greece and other emerging economies in eastern Europe also saw such credit insurance contracts freeze amid the broader uncertainty gripping the region and which forced local importers to put up the full cash amount of their imports before receiving the merchandise. "By September we will have reached exactly that point," he said.

Mr. Asimakopoulos said most businesses should be able to survive on their inventories and their existing cash reserves before that point. But he warned that Greek importers had already experienced problems receiving credit insurance since the beginning of 2012 and what happened last week was "the icing on the cake."

"The most important thing is that such actions create a climate of fear and panic and this is the most dangerous for the country's economy," he added.

He said there is already shortage in some specialty goods or labels--such as some brand name personal care products, for example--and that some companies that stock such products are already teetering.

"Some importing companies could collapse in the near future and this could lead to [shortages] problem until we have a successor importer," Mr. Asimakopoulos said.

At the same time, importers of raw materials, are also feeling the pain.

"This is blocking Greek merchants, it is a punishment of the country, because of the [ghost] of the drachma," said Vasilis Korkidis president of Greek retailers association, referring to the country's former currency.

"There is already shortages in raw materials, mainly in metals, which are not very obvious since the production is currently at low levels. But, if uncertainty remains there will be collapse of the domestic internal market by September," he said.

According to Mr. Korkidis, about 80% of products in the Greek market are imported. Since importers have to completely pay in cash, they will have to find EUR20 billion by the end of the year to cover those imports, something he describes as "impossible".

At the same time, many Greek companies--both importers and exporters alike--are facing a cash crunch as local banks have slashed lending in a bid to preserve their own liquidity.

For several months now, Greek exporters have also had to scramble to secure export credit guarantees from foreign banks after importers abroad stopped accepting those guarantees from Greek banks.

"Many companies are considering relocating their companies to neighboring Balkan countries in order to have cash flow from banks there," Mr. Asimakopoulos said.

-Write to Nektaria Stamouli at nektaria.stamouli@dowjones.com