Not actually sure if you can close the airfield, short of physically blocking the runway.
The employees of the local council who own the airfield are the ones going on strike - right?
They can't stop other employees of the same company going to work if they wish too. I doubt if they are allowed to stop employees of total different companiers from going to their own places of business which happen to be on the airfield.
So the only facility which may be withdrawn would be the A/G.
But - this is conjection based on my own experiences of industrial action. I'll be at work elsewhere so its immaterial.