[sokoloff]

An RSU is not exactly equal to an option with a strike of $0, because you control the exercise date on an option. Not so on an RSU.

The taxable event with options is the date of exercise (or the 83b election), not the date of vesting. The option owner has control over the date of exercise, meaning they can delay exercise until after the vesting date.

An RSU, having a "strike price" of $0, "exercises" (and therefore is a taxable event) the instant it vests.

In both cases, the gain (the surplus of fair market value over exercise price) is ordinary income and taxed as such.

In both cases, the gains (or losses) after the initial taxable event are capital gains, and the rules are not as simple as for stocks, but basically, for employees with typical vesting, hold the shares for a year after exercise and these gains are long-term capital gains.