The British Prime Minister David Cameron says he's seriously concerned about Spain's row with Britain over Gibraltar.
There have been complaints about excessive border checks, and now Spain's foreign minister has hinted they could impose a 50 euro cross-border fee.
David Cameron said none of the measures had been raised with the UK government.
Spain's latest move follows increased vehicle searches at the border last weekend, causing major delays.
Gibraltar's chief minister is accusing Spain of acting like North Korea.
Spain disputes UK sovereignty over Gibraltar, which has been ruled by Britain since 1713.
