No employee in the civil service shall in any manner be concerned in giving, soliciting and receiving any assessment or contribution for any political party or activity or for any candidate for public office, nor shall he take any active part in political movements or political campaigns, nor act as an officer in any political organization. This shall not interfere with the right of each employee to vote as he pleases and to express freely his opinions. Proof of this violation of this section shall be sufficient grounds for summary dismissal of the employee.