I found this situation. The LOS go through a ship and an asteroids fields and we wondered about it. Of course we resolve thathe the obstruction rule apply once but... is it right?

If yes... do not be a good house rule (or even oficial) an acumulative obstruction penalty?

From the Rules Reference, Page 8:

Obstructed

An attack is obstructed if line of sight is traced through an obstacle token or another ship that is not the defender.

If an attack is obstructed by one or more ships or obstacles, the attacker must choose and remove one die from his attack pool before he rolls dice during the “Roll Attack Dice” step.

• Squadrons do not obstruct attacks.

• If line of sight is drawn over an obstacle, the attack is obstructed even if the bases of the attacker and defender are touching.

Related Topics: Attack, Line of Sight, Obstacles

According to this, regardless of the number of obstructions, only one attack die is removed from the pool.

It's a binary state.

An attack is either obstructed or not, resulting in a loss of one die regardless of the number of obstructions.

Yup, it is or is not. There is no stack

Do, or do not. There is no try.