3.3 Past Vesting Service The Plan is not required to give Vesting Service for employment with an employer before it became a Contributing Employer. However, when a new group joins the Pension Plan, the Trustees, in their sole discretion, may credit Past Vesting Service based on past work performed with that employer. Customarily, if the Trustees have decided to grant Past Vesting Service for your group, you will receive credit for one Year of Past Vesting Service for each Year of Vesting Service you earn after the employer begins making Contributions to the Pension Trust on your behalf. In addition, Past Vesting Service will be credited only if you work at least 2,000 Contributory Hours within two years after the date the employer is first required to contribute to the Plan on your behalf. This two-year time period is extended if you are totally disabled with an onset date less than two years from the date your employer is first obligated to contribute to the Plan for you. If your employer withdraws from the Pension Plan, your Past Vesting Service may be cancelled.