Bismihi ta'āla
Yes, it is allowed, but jurists include it as one of the makruh things to do when with spouse. Some jurists also said that this is specific to the man. He can still have a top on, or cover himself with something.
One view is that this at a time that the intention to copulate is for conceiving a child, where all mustahab and makruh things should be observed, as angels could attend, and out of shyness to the angels. This view is based on a hadith from Imam al-Sadiq (a.s.), from the Prophet (s.a.w.).
And Allah knows best