The party said Moratino's visit effectively treats the territory as a sovereign nation.
Leire Pajin, a spokeswoman for Spain's ruling Socialist Party, said the "issue of sovereignty is not at stake", adding the visit was to help improve the life of Spaniards living in Gibraltar.
The foreign ministers agreed to expand communications links between Spain and the
colony, including a new ferry route between Gibraltar and Algeciras and a hot
line between the two cities to discuss bilateral issues directly.
Around 12,000 people cross over from Spain daily to work in the territory, and many others visit for tourism.
Gibraltar is a haven for shipping and offshore banking because of favourable tax laws.
In 2002, its inhabitants overwhelmingly rejected an Anglo-Spanish proposal for co-sovereignty in a referendum.