Answer:
If the new law reduces the rate of job separation without affecting the rate of job finding, then, the natural rate of unemployment will fall.
This is because of the formula
U / L = s / (s + f)
Where U is unemployment, L is labor force, s is rate of separation, and f is rate of job finding.
The reason why the rate of natural unemployment will fall is because if employees are harder to fire, companies will be more careful when hiring workers, since the cost of firing a worker is now higher.