Council and school support staff, as well as nurses across England and Wales, were beginning to cast their votes on potential strike action in response to pay disputes.
The ballots will decide if various workers will go on strike amid the cost-of-living crisis and continuing staffing issues.
More than a 330,000 council and school support staff are set to vote on protest action over what Unison, Britain's largest public-sector union, has called an inadequate pay offer.
Unison had called for an increase of 2 per cent above inflation, stating that since 2010 the value of local government pay has fallen by 25 per cent.
General secretary Christina McAnea said without the council and school support staff, "the services on which whole communities rely won't exist".
"Staff are leaving their jobs because pay is falling ever further behind and neighbourhoods will suffer," she added.
Simultaneously, nearly 300,000 members of the Royal College of Nursing (RCN) are being asked to renew their mandate for taking industrial action until the end of the year.
The RCN rejected the government’s pay offer last month, urging members to vote for striking to pressurise ministers into an improved pay award for nursing staff and enhance staffing levels.
RCN general secretary Pat Cullen said: "Once again, we have been forced to ask our members if they want to take to the picket lines in their fight for fair pay.
"The NHS is fraying at the edges. To improve care and address the shortage, the government must bring more people into nursing and keep them there by paying staff fairly."
No 10 Downing Street defended its stance, insisting the government had made its last offer on pay.
A spokesman said: “We have offered a fair and generous deal that the RCN themselves recommended to its members and subsequently accepted by the majority of other unions via the NHS staff council."
Strikes would bring about extensive disruption to public services across the country.
The results of the council and school support staff vote are expected in early July, while the nurses' vote will conclude on June 23.
