You can view the UPC assigned to your release on the 'Your Music' page.

Once logged in to your Record Union account. ​At the top right corner click Menu(≡) > Your Music > Submitted tab and all of your published releases that have not been taken down will be displayed.

Go to the release you want to check and besides the release date, you may locate the UPC. You may also click the 3 dots(⋯) on the upper right corner of the release in question > View detailed information. Here you'll find all the available information about the release, including the UPC.

Please see the images below for your reference.