London Underground (LU) drivers are threatening to strike if their concerns over safety and security in the wake of the London bombings are not addressed.
Unions want additional security measures
The Rail Maritime and Transport (RMT) union said it will consider balloting members if talks with LU bosses on Wednesday fail to reach agreement.
Drivers want assurances over staffing levels and extra security measures.
LU said it will work with everyone to try to ensure public transport is as safe as possible.
But Bob Crow, general secretary of the RMT, said: "Given the urgency of the situation... we will not be sitting on our hands."
LU managing director Tim O'Toole and senior police officials will be attending the security conference with union representatives.
Mr Crow said: "This gives the company another opportunity to demonstrate that it will put in place additional measures that we have been seeking to improve the security.
"Staff in the front line have acted selflessly and professionally following the recent bombings and they have serious concerns and proposals that deserve serious consideration."
RMT officials described a meeting on Friday as "disappointing" and had said its members would not strike but the union would support any that felt too at risk to work.
LU's Mr O'Toole said: "We are determined to continue to work together - following the advice of police and security services - to ensure public transport in London is as safe as possible in the new environment in which we live.''
Issues the RMT want addressed include the following:
- They want LU to drop plans to weaken or abolish section 12 - which came in after the King Cross fire and sets out minimum standards for safety on sub-surface trains
- A review of the present suspect-package procedure, known as HOT (Hidden, Obvious and Typical)
- Consideration given to strengthening driver cab bulkheads
- The return of guards to Tube trains
- A return to dedicated gate-line staff that patrol ticket barriers
- Fully trained supervisors to accompany any contract work on the network
- Better equipment, such as breathing apparatus, for train operators and station staff
- Clarification of the situation around amber alert - the RMT said on 7 July that LU closed the entire network on amber alerts but on Thursday the network remained open
Meanwhile, the Transport and General Workers Union (TGWU) met London mayor Ken Livingstone to discuss crew safety, on board security procedures, including CCTV and bus radios, as well as company security at garages.
Eddie McDermott, the TGWU's regional secretary for London, described the meeting as "positive".