Former Home Secretary Alan Johnson has said he is in complete agreement with Theresa May on the need to pass the Communications Data Bill before the general election.
He told the BBC's Andrew Marr Show: "We need to get this on the statute book before the next general election and I think it is absolutely crucial.
"Indeed I think it is a resignation issue for a Home Secretary if the Cabinet do not support her in this central part of what the security services do."
The Communications Data Bill - dubbed the "snooper's charter" by its opponents - would give security forces greater powers to monitor communications such as emails.
More top news
British cyclist Simon Yates has failed drug test but his team are blaming an "administrative error" over an asthma inhaler.
Two ambulances crashed leaving one driver dead and three people seriously injured.
A scandal-hit NHS trust where a teenager drowned in the bath is still failing to protect patients from risk of harm, a watchdog has found.