“If there is no offer in front of us before midnight on Tuesday we will keep to further collective measures,” a GDL spokesman said.
A strike by train drivers for both freight and passenger routes crippled rail traffic in Germany on Thursday morning, with hundreds of cancellations and countless delays reported across the country.
The union, representing 75 percent of Germany's 26,000 train drivers, is pushing for a salary increase for Deutsche Bahn employees and for uniform pay practices at the former monopoly and at competitors.
Following a series of temporary strikes in recent days, more than 90 percent of members voted for an indefinite strike on Monday.
So far employers have failed to present a negotiable proposal, GDL leader Claus Weselsky said Friday.
“Even after three temporary strikes and the collective measures in freight and passenger traffic the employers have not budged a bit,” he said.
But Deutsche Bahn denied this.
"We really don't know how many offers we can still make," a spokeswoman said.
"We're not refusing. It's the opposite. Deutsche Bahn is and remains ready to negotiate on a collective wage contract for all train drivers."
GDL must first reveal their specific wishes and return to the bargaining table, she added.