(Adds detail, union comment.) LONDON (Dow Jones)--The U.K.'s Communication Workers Union, which represents around half of BT Group PLC's (BT) 128,000 staff, said Thursday it is pushing ahead with a nationwide industrial action ballot after five hours of talks with the U.K. telecom firm broke down Wednesday. The CWU has made it clear that only a "significant improvement" on BT's original 2% pay increase offer for this year will end the dispute. But BT has refused to budge despite an increase in profit, big bonuses for senior executives and a 6% payout for shareholders. The CWU has issued notice to BT that ballot papers will be sent out June 18. The ballot will close July 5, and the result will be announced. If BT staff were to vote in favor, the CWU would have to give BT seven days' notice of a walkout. BT's revised offer, which was tabled Monday with the CWU, includes a 2% pay raise this year and a 3% raise in 2011, plus additional one-off payments. It also gave a guarantee of no compulsory redundancies among direct BT staff in the U.K. between now and the end of 2011. The CWU, which represents 55,000 of BT's 128,000 workers, is demanding a 5% pay increase this year. "BT's revised offer failed to make any material improvement in pay for 2010 which we have made crystal clear is the key to resolving this dispute. While we are happy to consider a two-year deal, there must be an improvement in pay for this year," said Andy Kerr, CWU deputy general secretary, in a statement. The last BT national strike was in 1987. BT wasn't immediately available to comment. -By Lilly Vitorovich, Dow Jones Newswires; 44-0-207 842 9290; [email protected] (END) Dow Jones Newswires June 10, 2010 08:45 ET (12:45 GMT)