Firefighters in England and Wales will join a one-day strike by public sector workers on 10 July, the Fire Brigades Union has announced.
More than a million council staff, health workers, teachers and civil servants are expected to take industrial action on the same date.
The FBU is involved in a row over pensions and retirement age.
The government said fire authorities had "robust and well-tested plans that include back-up support if needed".
Firefighters have been involved in a series of strikes over the past year but the dispute remains unresolved.
The FBU strike is due to take place between 10:00 and 19:00 BST and will be the 15th in the firefighters' campaign. The union is expected to announce further action later this week.
General secretary Matt Wrack said: "The FBU has wanted to settle our dispute for a long time, but the government at Westminster is simply not listening. We are therefore proud to take strike action alongside our colleagues in other unions on 10 July.
"The fact that this government has united so many workers to take strike action against them is a testament to the failure of their policies. They are destroying our public services and wrecking the lives of millions.
"If they won't listen and won't negotiate, then this is the result and they should face more of the same if necessary."
The FBU has launched a legal challenge against the government's proposals, claiming that reducing the pensions available to firefighters by different amounts depending on when they retire after the age of 55 amounts to age discrimination.
Fire minister Brandon Lewis said public safety would "remain the primary focus".
He added: "The government believes a solution can be reached, but not under the shadow of industrial action, which only serves to damage firefighters' good standing with the public. By calling more strikes during an open consultation the FBU leadership has once again shown it is not serious about finding a resolution.
"The deal on the table is fair and gives firefighters one of the most generous pensions in the public sector. Additionally the proposals protect the earned rights of a higher proportion of members than any other public sector scheme. Nearly three quarters will see no change in their pension age in 2015."
The day of action on 10 July is part of a series of disputes with the government over pay and other issues.
Workers who have already said they will take part include civil servants in the Public and Commercial Services union, council and school support workers in the GMB and Unison, and members of the National Union of Teachers.