The allegation came days after the US enacted unilateral sanctions over Iran's nuclear programme, to penalise foreign companies trading with Tehran.
Britain said it was not aware of any refusal to refuel Iranian planes, and Germany stressed there was no ban.
Oil firms contacted by the BBC said they could not comment on individual contracts.
Tehran says its nuclear industry is for peaceful purposes but Western powers fear it is trying to develop a bomb.
"Since last week, our planes have been refused fuel at airports in Britain, Germany and UAE because of the sanctions imposed by America," Mehdi Aliyari, secretary of the Iranian Airlines Union, told Iranian media.