To be traitors to the Commonwealth
After the Clubmen risings through the Counties, and seeing the threat of a 3rd party coming to strength, parliament issued a law against any gathering barring arms.
On the 23rd August 1645 A "Declaration against the Club-men; and forces assembling without authority of Parliament" was read out.
"The Lords and Commons do declare all person or persons whatsoever, that shall associate or assemble themselves together in arms, in any parts of the kingdom, without authority of Parliament, to be traitors to the Commonwealth, and to be proceeded with accordingly; and that the governors and commanders of all garrisons and places under the power of the Parliament do publish this declaration, and use their best endeavours to prevent and suppress any such associating or assemblies, and to seize upon the heads or the leaders of them.
Ref.. The Parliamentary Or Constitutional History of England