Prime Minister David Cameron and the Foreign Office have said they are concerned about comments made by Spain's foreign minister.
Jose Manuel Garcia has suggested a 50 euro fee for crossing the Spain-Gibraltar border could be imposed.
There have also been complaints about excessive border checks causing delays in and out of Spain.
The latest tension has flared up around an artificial reef, which Madrid claims is harming their fishermen.
The Rt Rev Ralph Heskett is the Catholic Bishop of Gibraltar.
He spoke to Premier's Marcus Jones on the News Hour, about the impact a border-fee would have on local people: