We the people should have the major voice and influence on government, not the highly financed lobbyists funded by big business, corporations, trade organizations and unions.
Citizens should be the only ones allowed to fund lobbying activity and to keep the playing field level, there needs to be a cap on how much funding can come from each individual citizen. This would prevent the very wealthy from drowning out the voice of the middle class and the poor.
Restricting the funding to citizens would then exclude business and union entities. This is not to say their voices would be silenced, just that the citizens in those businesses or unions would need to fund the lobbying directly as private citizens with a common interest.