"Strike ballots" refers to voting by workers to decide whether or not to go on strike, which is a form of protest where employees collectively choose to stop working until their demands are met by their employer. Full definition
The bill includes a requirement for a 40 % turnout threshold for strike ballots in «important public services». (bbc.co.uk)
The Conservative party is considering plans to introduce a threshold which could prevent many strike ballots from resulting in legal industrial action. (politics.co.uk)
New strike ballot voting thresholds of 40 % will make most industrial action illegal — this from a government backed by less than 25 % of the electorate. (theguardian.com)