The RMT says the Metronet's offer has angered members

Metronet said that in order to avoid lengthy negotiations it will pay the increase now, backdated to 1 April.

But the Rail Maritime and Transport (RMT) union said the company is imposing the rise to avoid further talks.

LU workers and the other private firm, Tube Lines, are also being balloted, with the results due next week.

Metronet denied it was imposing a deal on its workers and said it would be meeting unions on Friday.

Metronet's attempts to impose a settlement will prove to be counter productive RMT's Bobby Law

The company, which maintains nine of the 12 LU lines, said it was surprised to receive a notice last week from the RMT warning that the two sides were in dispute and that workers were being balloted for strike action.

A Metronet spokesman said: "A long drawn out settlement would erode earnings through inflation and, in the event of industrial action, erode earnings further.

"This is bad for everyone. We have listened to staff and have decided to take a positive step forward."

Bobby Law, the RMT's London regional organiser, said: "Metronet's attempts to impose a settlement will prove to be counter productive.

"There have been no offers, no talks, absolutely nothing. Our members are already angry.