Welsh-based CommsDirect, who sell 3G mobile phone contracts, said they intended to take advantage of the "once in a century" opportunity to have global television exposure at the Wembley fixture between Cardiff and Portsmouth.
Matt Burge, managing director of CommsDirect, has said they were approached by a sports marketing agency representing an undisclosed online gambling business based in Asia three days after Cardiff's semi-final win over Barnsley.
The agency offered £500,000 to have its clients' name emblazoned on Cardiff's strip for the final instead of CommsDirect.
Mr Burge said: "The offer of £500,000 was tempting, but after discussing it with our board and then with Cardiff City we decided to reject it."
He said that Cardiff City's financial director left the decision up to CommsDirect.
However the company had 'some serious reservations': "We couldn't really envisage fans turning up with CommsDirect on their shirts only to see the players running out onto the pitch with a different name on theirs. That would have looked bad for us."