Elon Musk ended a customer referral program that included free electric charging for Tesla buyers because it’s adding too much cost to the vehicles.

The offer will end on Feb. 1, Musk said in a tweet. Model 3 costs are being especially affected, the Tesla Inc. (TSLA.O) chief executive officer said in a subsequent reply on Twitter.

According to a December report on the Electrek website, Tesla previously extended the program to March 11. Buyers received six months of free supercharging and Tesla owners were given rewards depending on the number of referrals, the report said.