Untrue. A Club’s “Salary Cap Threshold” shall be 40 % of the Club’s gross annual operating budget for that Salary Cap Year, as set out in the Club’s 2014 – 2017 FAWSL Club Licence. This figure must be agreed with the FA WSL Business Manager by such date as is notified by The Football Association in each Salary Cap Year.
Essentially the budget could be unlimited, depending on how seriously City take it.
That's the rule they have in place to prevent teams from offering million pound salaries to entice their highest earners. The 20k rule still applies though.
http://www.fawsl.com/news/faqs_15_to_20.html#UXRUUGKUZGbSfIip.97