Workers on the London Underground (LU) have been told they will not be paid if they refuse to work during the next firefighters' strike.

In a letter to staff, the company said it is confident the network is safe.

The Rail Maritime and Transport (RMT) union has reacted angrily to the threat.

It has already warned LU that its members will be balloted for strikes if disciplinary action is taken against those who refuse to work.

Stations closed during strike

Belsize Park Borough Caledonian Road Chalk Farm Covent Garden Edgware Road (Bakerloo Line) Elephant & Castle Goodge Street Hampstead Holland Park Holloway Road Kennington Lambeth North Lancaster Gate Mornington Crescent Queensway Regent's Park Russell Square Tufnell Park Wapping

About 350 of LU's 15,000 staff refused to work during the two-day strike last week because of concerns over safety.

Most of them were drivers - more than 100 of those were RMT members and up to 200 were members of the drivers' union Aslef.

LU says it has addressed the safety concerns of those who walked out and is sure the network is safe.

The RMT has notified LU that it will send ballot papers to 8,000 Tube workers next week. A result is due on 12 December.

Staff shortages

Aslef said it was not clear whether withholding pay would be regarded as disciplinary action.

During the firefighters' 48-hour strike staff shortages led to the suspension of the Waterloo and City line on Thursday and of the Circle line on Friday.

Other services were disrupted or restricted and 22 deep-lying stations were closed by LU following a safety assessment.

An eight-day strike by firefighters is due to start at 0900 GMT on Friday.