The government's second largest department has gone back on its promise to retain check-off.
HM Revenue and Customs bosses say they will withdraw the system for collecting union subscriptions through salaries at the end of April.
This comes just a day after their latest announcement of hundreds more job cuts.
With staff told last August that check-off would remain, this news is further evidence of an increasingly anti-union approach being adopted in the department and elsewhere in the civil service.
We know from a leaked memo that senior HMRC officials want to undermine our influence at a time when we are campaigning against damaging cuts and office closures.
In the run up to a general election this is a deeply irresponsible approach, given Labour and the Liberal Democrats have indicated they would restore check-off, which has been in place for decades.
We are urging all our members to sign up to pay their subs by direct debit and retain the protection of our union.
General secretary Mark Serwotka said: “This is the greatest challenge our union has ever faced.
“We are clearly being attacked because we continue to oppose this government's ideologically driven and damaging spending cuts.
“We will not be silenced, we are determined to put trade union rights at the centre of the general election this year.”