If a levy is imposed by the government it is essentially the same thing as a tax.
However, a union, club, organisation or association could decided to raise a levy, and that could not be called a tax.
For example, a football club could have membership fee of $100 a year. One year there is a severe storm, and the club's roof is damaged. The club could decide to raise a special levy of $20 per member to pay for the storm damage.