If the cargo is contaminated, polluted air may penetrate the ISS through the hatches, which were due to be opened around 1000 GMT on Monday.
Since ESA's automated transfer vehicle (ATV) is docked with the Russian segment of the station, the Russian part of the ISS crew took air samples from inside the ATV for examination.
Around 1200 GMT, an emergency conference began at the mission control center, which is situated near Moscow, and during it Russian mission control staff discussed the problem with Houston, Texas, through a video link.
No decision has been reported so far, and an item on the ATV website says the problem may take up to several days to solve. The hatches will remain closed meanwhile.
Voice of Russia, IF