An emergency debate on Tube maintenance will be held by the London Assembly, after safety fears caused major delays on the Northern Line.
London Underground oversaw repairs
Almost half the line's fleet was out of service on Friday because emergency brake systems had to be checked.
London Underground (LU) used emergency powers to oversee remedial work by Tube Lines and its subcontractor Alstom.
But London Assembly Lib Dems and Tories say LU should have taken over repairs as passenger safety was compromised.
An LU spokesman said it felt the appropriate action had been taken at this time.
He also explained that it had taken an emergency directive out on maintenance contractor Tube Lines which in turn had taken one out on Alstom.
Tube Lines inherited the maintenance contract for the Northern Line from LU.
But Lib Dem Geoff Pope said: "When passenger safety is compromised on a Tube line, immediate action must be taken including bringing maintenance back in house to fix the problem.
"London Underground should exercise its rights and take control of the repairs whenever passenger safety is put at risk."
A spokesman for Tube Lines said it had provided LU with a full fleet of trains since Saturday and that it was dissatisfied with Alstom's performance.
Alstom said it had been working closely with LU and Tube Lines.