Transport for London has said there will be "no visible impact" on the line, which connects Bank and Waterloo, as a result of a strike by staff working in its control room.
"Due to detailed planning there will be no visible impact on the network should this unnecessary strike action go ahead.
"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," said the line's operations director Peter McNaught.
RMT members voted in favour of a 48-hour walk out starting on Monday (28 September) evening over pay. TfL claims just three people voted in favour of the strike, out of six staff who are union members and eight working in the Waterloo and City line control room in total.
RMT boss Mick Cash said last week: "London Underground (LU) management must be clear by now on our members legitimate and reasonable demand for re-grading.
"The union has re-iterated 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. Although LU has declined our request for arbitration at Acas, they are aware that as always we remain available for talks to resolve the dispute."