CORRECTED-Strike slows shipping at two Panama canal ports

(In Sept. 2 article, please read in first paragraph and throughout story that strike was by tow boat crews, not crane operators. Corrects in 1st paragraph that ports, not canal traffic, affected)

PANAMA CITY, Sept 2 (Reuters) - Tow boat crews at two major Panama Canal ports went on strike on Tuesday to push for better pay and conditions, slowing shipping in the ports, shipping firms and the labor ministry said.

Roughly two thirds of tow boat crews in Balboa and Cristobal ports were not working, leaving a backlog in loading and unloading containers and hitting the flow of everything from Chinese-made electronic goods to European farm produce.

Union leaders could not immediately be reached and it was unclear how long the strike could last.

Balboa, at the Pacific entrance to the canal, is one of Latin America's biggest ports. Cristobal is one of a handful of ports on the Atlantic end of the canal and one of the most-used for container ships.

An official at the company operating the tow boats, a division of Amsterdam-based Smit Internationale (SMTNc.AS), said a skeleton crew had come to work.

"Even if they are on strike, 30 percent have to work," Smit commercial administrator Rupert Britton told Reuters.

Shipping agent C.Fernie & Co, which has offices at both ports, said the limited boat movements were not enough to maintain normal levels of trade.

The ports, run by Hong Kong's Hutchison Whampoa (0013.HK), are used by shipping giants like Denmark's A.P. Moller-Maersk (MAERSKb.CO) for loading and unloading cargo and maintenance.

Around 5 percent of global trade passes through the Panama canal and the waterway accounts for a fifth of Panama's gross domestic product. (Reporting by Andrew Beatty; Editing by David Gregorio)