It is the second Union game called off this season after their fixture against Bayern Munich in December was postponed due to heavy snow and rescheduled for January 24th.
"The reasons for this (postponement of Mainz v Union) are the ice forming in the lower parts of the stands, especially the standing tribune, as well as access roads for spectators," the DFL said.
A new date will be set soon. Mainz are 16th and in the relegation play-off with Union 15th, three points ahead.
Freezing rain in central and southern Germany in the past few days has grounded hundreds of flights and restricted train traffic on Wednesday as the weather service warned of slippery roads and heavy snowfall.
The weather service added that there was an extreme risk of black ice and heavy snowfall in the affected regions, while German rail operator Deutsche Bahn has warned of delays and cancellations in view of the winter weather.
