Britain faced its biggest rail strike in 30 years that crippled the transport network in June.
Crunch talks are at a deadlock between the company and the unions.
In the wake of the latest deal, the Rail, Maritime and Transport Workers union (RMT) said it equates to a real-terms pay cut over the next two years.
They also said the offer would see a cut to a third of frontline maintenance roles and half of scheduled maintenance work.
RMT general secretary Mick Lynch said on Tuesday the new offer was dependent on productivity and modernisation clauses.
He said: “It amounts to a real-terms pay cut for members over the next two years and would cut a third of all frontline maintenance roles and half of all scheduled maintenance work.
“There is also a wholescale expectation of unsocial hours and lower pay across the board. Network Rail has offered high level managers a huge hike in salary in return for very modest flexibility compared to what you and your colleagues have been offered.
“All companies involved in this dispute need to understand that key railway workers have lost thousands of pounds in earnings due to a pay freeze in recent years – and rightly, you refuse to be short-changed again.
“Settlements reached with London Underground and recently Merseyrail are also well in excess of what you have been offered here.
“We will not hesitate to call further strike action and co-ordinate this with other trade unions if the industry continues to fob us off with unacceptable offers.”
Talks between the RMT and train operators were taking place on Tuesday evening.
The RMT Executive Committee will meet on Wednesday to discuss its next move.