Three new strike dates on Northern trains
Members of the Rail, Maritime and Transport union will walk out on October 6, 13 and 20.
They will also walk out on October 5 and 6 at South Western Railway.
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Hide AdSouth Western Railway said it was "disappointed" by the decision.
The union accused SWR of refusing to engage in serious talks.
Northern was accused of failing to give assurances on the guarantee of guards on its services.
Talks between the RMT and Northern ended without agreement on Wednesday.
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Hide AdRMT members at SWR recently renewed their support for industrial action in a ballot.
Union general secretary Mick Cash said: "The company has continued to fail to provide any offer that comes close to resolving this dispute and their latest attempts at delaying talks has not gone unnoticed."