London faces another Tube strike as staff on the Waterloo and City line plan to walkout for 48 hours from 28 September in a dispute over pay.
The service control workers are members of the Rail, Maritime and Transport Workers (RMT), which is one of four unions still in negotiations with Underground bosses over the Night Tube.
The union said 100% of its members on the lines vote in favour of the strikes as part of a re-grading dispute. The staff have been asked to not work from 9pm BST on 28 September until 11pm BST on 30 September.
"LU management must be clear by now on our members' legitimate and reasonable demand for re-grading. The union has reiterated that we will not accept an offer which is based on a change in staff duties or which would cause a detriment to other members," said Mick Cash, the RMT general secretary.
"Although LUL has declined our request for arbitration at [mitigation service] ACAS, they are aware that as always we remain available for talks to resolve the dispute."
But Transport for London (TfL) said it would work to minimise the impact of the planned industrial action and argued that managers had proposed "various options" to RMT negotiators in bid to end the dispute.
"These have included exploring development opportunities to help progress the careers of the staff concerned as well as allocating additional responsibilities that would justify a salary increase," said Peter McNaught, an operations director for the Waterloo and City lines.
"Unfortunately all of these options have been rejected outright by the RMT who appear determined to demand more money for no additional work or responsibility. We remain committed to discussions with the RMT representatives and I urge them to consider the options we've proposed rather than threaten industrial action."
LU also alleged that only three union members voted for the strike action, a comment an RMT spokesman reacted to by warning Underground bosses to not "denigrate" or "underestimate" the strikers.
"It is a small team of staff same as every other service control room but LU would be foolish to denigrate them or underestimate both their anger and the potential impact of the action," the spokesman said. Unite, Aslef and the TSSA are not involved in the Waterloo and City line pay dispute.