Staff at leading housing charity Shelter are to stage a three day strike in a row over pay.
Unite said its 400 members will walk out from next Tuesday in protest at cuts of up to £5,000 for frontline staff.
The action, hitting the charity's advice and support work, was backed by two thirds of those taking part in a recent strike ballot.
Unite has also accused Shelter of proposing pay changes which it said will create a two tier workforce.
Shelter's main offices in London, Glasgow and Sheffield as well as smaller ones in cities such as Manchester and Bristol will be affected by the three day strike.
Unite regional officer Peter Storey said: "Our members care deeply about the help they give and the people they support. They are fearful that 'cut rate pay' will lead to a 'cut rate organisation' as managers struggle to recruit experienced replacements on the new lower rates of pay.
"Shelter's frontline support and advice workers are the lifeblood of the charity and deserve better than pay cuts while those with huge salaries at the top see their pay protected.
"Cutting pay for some of our lowest paid staff is simply not necessary. Shelter is in a healthy financial position and management need to get back around the table to negotiate a fair settlement."
Shelter chief executive Campbell Robb said: "We are disappointed to learn that Shelter's union members have voted in favour of taking industrial action. While only a small proportion of our staff have voted in favour of strike action, we have developed contingency plans to ensure there is as little impact as possible on the services we provide.
"At Shelter we aim to pay a broadly typical market salary across all roles and we benchmark salaries regularly to help us achieve this. In doing so we have found we currently pay staff working in advice and support well above the salary for similar roles elsewhere, which with funding cuts and more competition for donors we cannot sustain.
"This leaves us with a simple but painful choice: keep the higher pay levels, cut our services and make some roles redundant, or maintain the number of people we help and reduce salaries for new staff. We always strive to be the best employer we can be, but in this instance we feel we have to put our ability to help those who need it first."