(1) Each firefighter participating in the retirement system shall contribute to the retirement system a sum equal to six and one-half percent of his or her salary. Such payment shall be made by regular payroll deductions from his or her periodic salary and shall be credited to his or her employee account on a monthly basis. Each such account shall also be credited with regular interest.
(2) Each city of the first class with firefighters participating in a retirement system shall pick up the firefighters' contributions required by subsection (1) of this section for all compensation paid on or after January 1, 1984, and the contributions so picked up shall be treated as employer contributions in determining federal income tax treatment under the Internal Revenue Code, except that the city shall continue to withhold federal income taxes based upon such contributions until the Internal Revenue Service or the federal courts rule that, pursuant to section 414(h) of the Internal Revenue Code, such contributions shall not be included as gross income of the employee until such time as they are distributed from the retirement system. The city shall pay the employee contributions from the same source of funds which is used in paying compensation to the employee. The city shall pick up the employee contributions by a salary deduction either through a reduction in the cash salary of the employee or a combination of a reduction in salary and offset against a future salary increase. In no event shall a firefighter be given an option to choose to receive the amount of the required contribution in lieu of having such contribution paid directly to the retirement system.
(3) Each firefighter participating in the retirement system shall be entitled to make voluntary cash contributions to the retirement system in an amount not to exceed the contribution limitations established by the Internal Revenue Code. Voluntary contributions shall be credited to the employee account and shall thereafter be credited with regular interest. A voluntary contribution shall become a part of the Firefighters Retirement System Fund and shall be held, administered, invested, and distributed in the same manner as any other employee contribution to the retirement system.