According to their Facebook page:
If you're not one of the 683 people who have signed up for the #ValueUs Thunderclap tomorrow morning, (a) you're missing out on the fun and (b) you have just over seven hours to do so.
The response so far has been incredible. The total reach of those signed up is currently an amazing 461,838.
You can sign up on Facebook as well as Twitter.
Basically, a Thunderclap sends out the same tweet or Facebook post hundreds and thousands of times, depending on how many people sign up for it, all at the same time.
In this case, it will be 7.30am on Tuesday, the first strike day.
By signing up to the Thunderclap, you are giving your consent for the message to be sent from your account (you can do it from Twitter, Facebook or both) at that precise time, so you don't have to be there, tweeting, it does it automatically.
All these tweets going out at the same time causes a "thunderclap", which makes people on Facebook and Twitter take notice.
A lot of people will then retweet or share, causing a bit of a Twitterstorm following the Thunderclap.
It's clever stuff, but we need as many people to sign up as possible, so please share the link below with your friends and family.
This is the message which has been chosen to go out:
"#Solidarity to Durham TAs on strike 8-9 Nov vs Durham County Council's fire & rehire policy & 23% pay cuts #ValueUs" with a link to the Justgiving donation page.
When you sign up to the Thunderclap, you can also choose to share it on Twitter or Facebook, and it will inform those following you, encouraging them to join in.
Sign up here.