The ballot will open on Monday 19 June and close on Wednesday 5 July. Prospect's BT committee is seeking a mandate from members to enable it to put pressure on BT to come back to the negotiating table.
National secretary Philippa Childs said: "Not only do we believe that BT's position is divisive, it is also unprecedented. Earlier this year we reached agreement to pay team members increases of 2.6% over 15 months. Team members also receive overtime payments and guaranteed pay progression.
"The company's view is that this year's reduced bonuses for the Reward Framework compensate for a freeze on base pay. But we know that it does not make up for the extra hours and level of commitment that our members demonstrate consistently.
"BT argues that it is making some increases to base pay by implementing the equal pay review and starting pay on promotion (ie part of your terms and conditions of employment).
"RPI is currently running at 3.7% and CPI at 2.9%, so a pay freeze represents a cut in pay in real terms for Prospect members in the Reward Framework. Furthermore BT has failed to acknowledge and address the issues around pay differentials, pay progression and market levels of pay.
"The response from members so far has been very encouraging and we have had a sharp increase in membership applications.
"Our meetings and conference calls have been well supported across the business, so the next step is for us to be able to demonstrate to BT that we are speaking with the full support of members.
"This challenge is one of several that are facing members: the review of the Reward Framework, potential changes to the BT Pension Scheme and managerial job losses. Now is the time for us to demonstrate our collective strength and give Prospect a mandate to explore all possibilities to bring BT back to the negotiating table.
"At this stage we are only asking for your reaction to the pay freeze. Once we have a result we will do all we can to seek a negotiated settlement. Should that be unsuccessful we may have to ballot you again to see what further action you are prepared to take. So this ballot is the first step in our campaign.
"Please endorse the BT committee's position and vote to reject the freeze on basic pay by BT. Thank you for your continued support.
"You will shortly receive a separate email with your unique logon details and a link to the snap ballot in order to cast your vote. If you do not receive an e-ballot within the next 24 hours then please email email@example.com," Childs concluded.