Now, with Clinton out of the race, and Obama working hard to bring the New York senator's supporters over to his side, he's facing frustration by many Clinton supporters over how the Florida and Michigan mess was resolved.

CNN: Obama's path to presidency goes through Michigan

But now Conservatory Lab is facing dwindling union interest among its teachers and growing frustration over its affiliation with the federation, which frequently attacks the academic accomplishments of charter schools and last year tried unsuccessfully to block an aggressive expansion of these schools.

FORBES: Will Conservatory Lab Charter School Stay Unionized?

They also warned that staff were facing an increasing number of assaults because of high levels of frustration being built up by the delays.

BBC: NEWS | UK | JobCentre staff in 48-hour strike