Commuters face possible disruption next week because of an overtime ban by railway maintenance workers.
The Rail Maritime and Transport Union said its members at maintenance firm Balfour Beatty, who are contracted to Railtrack, will begin an overtime ban on Tuesday in a dispute over terms and conditions.
The proposed action coincides with the start of the "leaf-fall season", traditionally a difficult time for rail companies who face problems with leaves on their lines.
Bob Crow, the union's assistant general secretary, said: "We have been negotiating with the company for some time, but we have drawn a blank.
"Despite making massive profits, management is trying to undermine our terms and conditions."
He added that rail services for Sussex commuters travelling out of the county would be hit, but rail firms insisted measures are being put in place to prevent disruptions.
Connex spokesman David Ewart said: "We cannot comment on what disruption the overtime ban will have on services, but we have been working very closely with Railtrack to ensure that every precaution is made to avoid any inconvenience."
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