The Home Office says trade union activism and political canvassing should count towards the planned new system of 'earned citizenship'.
Migrants who complete 50 hours of voluntary work will be entitled to receive British citizenship after six years - two years earlier than if they do nothing.
Ministers had originally given examples such as running a local scout group rather than helping unions such as the RMT, which this week inflicted crippling strike action on London.
Critics will point to the historic relationship between Labour and the unions. Migrants cannot vote until they become citizens - so, by using union membership to speed their applications, Labour is potentially swelling its own support.
The details emerged in a Home Office document circulated among MPs this week. It reveals that employers will be expected to give people time off, where required, to complete the service.
Shadow Immigration Minister Damian Green said: 'This Government seems to think that standing on a picket line or handing out political leaflets should give people a fast track to a British passport.
'These are half-baked ideas which show that at best Ministers are making up policy as they go along.
'This sort of proposal threatens to bring the whole idea of earning British citizenship into disrepute.'
The list of activities which count towards earned citizenship includes trade union activities and canvassing for a political party - which also covers the Tories and Liberal Democrats.
Even aiding the BNP would count - if it was willing to accept help from an immigrant.