In a statement, the RMT said it has asked for the railways inspectorate to "investigate Network Rail's decision to scrap testing scheduled to take place on Friday June 13 – risking missing urgent track defects until the following Monday."
They also claim that, "electrical switching and power isolation is to be undertaken by managers who may not be fully competent to carry out such safety critical tasks, potentially also posing serious risks to staff working in electrical control rooms."
The RMT-sponsored strike by 12,000 maintenance workers will begin at midday on Saturday.
RMT General secretary Bob Crow said, "We are used to employers disregarding safety during industrial action, but this is the first time I can remember it happening before industrial action has even commenced.
"This decision is astonishing and deeply disturbing because urgent defects that would normally be picked up on Friday will now remain undiscovered until Monday June 16, and that will put other rail workers and passengers at serious risk throughout the weekend.
"The only possible reason for Network Rail’s decision is that they simply do not want to know if track is in an unsafe state, because it would mean putting emergency speed restrictions in place or re-routing trains.
"I have asked the railways inspectorate to investigate this matter urgently, and I have also urgently asked train operators what they intend to do under the circumstances, as they also have responsibilities for the safety of their staff and passengers.
"The use of hastily trained managers to undertake safety-critical electrical switching and power isolation during the strike also raises serious concerns for our operational members working in electrical control rooms.
"The union has made it clear to members that if they believe they are in serious and imminent danger they have the legal right to invoke Worksafe procedures and request alternative duties, and if there is any victimisation as a result there will be an immediate ballot for industrial action," he said.