Some people misunderstand this and this is a famous myth. However, please do not worry, this is not correct. Your tax is calculated from your taxable income and the number of jobs is not relevant. If you earn $50,000 from one job or from four jobs, taxable income is same $50,000.
The reason why some peopel think this is a higher tax withhelding rate should usually be used from the second job. If you do not ask your employer to use ahigher tax withholding rate, you often receive a tax bill rather than a refund at a tax return lodgement. Or as higher tax withholding rate is often used for the second job resulting in lower net wage, you feel you pay more tax. Regardless of this, it is recommended that you should use a higher withholding rate from the second job.