The UK Government has announced it is considering taking legal action against the Spanish, after they imposed new border checks on those travelling into and out of the British Overseas Territory, reports the BBC.
The Spanish Government has recently increased the number of border control checks on vehicles entering and leaving the British-held enclave, resulting in long queues and major disruption to residents and holiday-makers.
Spain says the checks are necessary to stop smuggling and believes that they represent a 'proportionate' response to a legitimate threat, the legal test that would be applied should any legal action by the UK be forthcoming.
However, the timing of the new tighter border controls is controversial, coinciding with a row between the Spanish Government and Gibraltar over their construction of a new artificial reef which the Spanish claim will heavily disrupt fishing in the local area.
A spokesman for the UK Government said they believed Spain's actions at the border were 'politically motivated' and that legal action was a possibility.
"This would be an unprecedented step," said a spokesperson for the UK Government.
"So we want to consider it carefully before a making a decision to pursue," they added.
Any legal challenge is likely to focus on Spain preventing the free movement of goods, services and people into and out of Gibraltar.
Freedom of movement is a key tenet of EU law.
Locals have described how the Spanish border checks are resulting in queues of up to seven hours in stifling heat and that the checks seem to be focused on weekends when tourist traffic is at a peak.
The European Commission has announced that it will investigate the new border patrols, but a team is unlikely to be deployed to the region until next month.