Pat Cullen, general secretary of the Royal College of Nursing (RCN), spoke to nurses during a visit to a hospital in Guildford, Surrey, on Monday, as union members continued to vote on whether to continue taking strike action over pay and staffing until the end of the year.
The ballot ends on Friday.
She told the Guardian: “Talking to nurses today, it is clear that they are unhappy with how they’re being treated and feel the NHS is on a precipice.
“After nurses said they needed better from Government, they can vote again on whether to take more strike action until December.
“There are only a couple of days left to vote by post and it is starting to look like the Government’s rules on postal voting could get the better of us.”
She said she believed the ballot would indicate support for further strikes but the 50% voting threshold may not be reached.
She added: “Nursing staff can still post their ballots back but unless 150,000 people get their votes sent back in the post then the strike has hit the end of the road.
“Secure online voting was used to select a new Conservative prime minister last year so it is clear they just want to make it harder for working people to have their voices heard.
“For the rest of the week we’ll be visiting hospitals and reminding people that if they want to keep the pressure on the Government they have to think of the post box like a ballot box.”