Nicholls stressed the refusal felt like a “step backwards” and implored the country “simply cannot afford” the continuation of this level of “economic pain”.
She said: “It’s so frustrating we now seem even further away from this dispute being resolved.
“A functioning rail network is one of the most important pillars of infrastructure in the country and it’s critical for so many consumers, workers and businesses.
Last week saw RMT decline revised proposals from Network Rail and the Rail Delivery Group to settle ongoing disputes, claiming the offer would mean real terms pay cuts for its members and unsafe working conditions.
RMT general secretary Mick Lynch said: "We have carried out an extensive listening exercise and our members have spoken.
"If our union did accept these offers, we would see a severe reduction in scheduled maintenance tasks, making the railways less safe, the closure of all ticket offices and thousands of jobs stripped out of the industry when the railways need more investment not less.
"It is now time for the employers and the Government to listen to railway workers in their tens of thousands.”
Lynch concluded the industrial campaign would continue “for as long as it takes to get a negotiated settlement that meets members reasonable expectations on jobs, pay and working conditions”.
Furthermore, RMT stated it would soon begin making preparations for a re-ballot when the existing strike mandate expires in May.
Nicholls added: “I again urge all involved in the negotiations to double down on reaching a resolution as soon as possible, to avoid inflicting even more pain on an already embattled sector.”