Tesla CEO Elon Musk is extending the company’s referral program by removing a limit and adding an extra bonus.

The program began earlier this year, rewarding Model S owners around the world for any referrals that resulted in a finalized sale. Under the program, if someone refers a buyer, they receive $1,000 to use towards a new car, service or an accessory. When someone uses a referral link to buy a Model S, that person gets $1,000 credit off the purchase price of the sedan.

In addition, the first person to make 10 successful referrals in each sales region receives a free Model X.

According to Musk, this program has been so successful that the company is expanding it. He sent a letter to Model S owners with more details.

“As you know, the Model S referral program was designed as an experiment, and so far it seems to be working,” said Musk in the letter. “So, we’ve decided to remove the 10-referral limit. From now until the end of the program, you can refer as many friends as you’d like. Your link will continue to work until October 31st. What’s more, we’ve added an additional reward: the customer who makes the most referrals by the end of October will be invited to swap their current Model S for a fully loaded Ludicrous P90D Model S, for free. All other terms of the program remain unchanged.”

Other rewards under the program include:

  • Five referrals earns owners a free Tesla Powerwall, including installation. As a bonus, they receive two tickets to the grand opening party of the Gigafactory.
  • Ten referrals gives owners the chance to purchase “a fully loaded Founder Series Model X, which is not available to the public, for the price of a base-level Model X – roughly a $25,000 saving.”

Bjorn Nyland, a Model S owner in Norway and the creator of popular YouTube videos about the car, became the first to win a Model X. Nyland won’t receive his new Tesla until all 10 referrers take possession of their new cars, which could take a few months.

SEE ALSO: Musk: First Tesla Model X Deliveries Set For September 29

But not everyone is happy about the program. The California New Car Dealers Association argued the Tesla is illegally “bird dogging,” which pays people who coordinate a sales without a license.

“While many other licensed dealers would like to offer similar referral fees to existing customers, California law flatly prohibits the practice,” states a complaint letter from the organization to the California Department of Motor Vehicles. “Tesla is required to abide by the same consumer protection rules that apply to all other vehicle dealers in California.”

Tesla, however, feels that it is not breaking any rules with the program.

“We looked carefully at those regulations,” Tesla representative Ricardo Reyes said in response. “They were enacted decades ago to prevent rogue salespeople, not from preventing friends from recommending products they love.”