Tesla confirmed the price change in a statement:

“Moving beyond the success of Q4, we are taking steps to partially absorb the reduction of the federal EV tax credit (which, as of January 1st, dropped from $7,500 to $3,750). Starting today, we are reducing the price of Model S, Model X and Model 3 vehicles in the U.S. by $2,000. Customers can apply to receive the $3,750 federal tax credit for new deliveries starting on January 1, 2019, and may also be eligible for several state and local electric vehicle and utility incentives, which range up to $4,000. Combined with the reduced costs of maintenance and of charging a Tesla versus paying for gas at the pump – which can result in up to $100 per month or more in savings – this means our vehicles are even more affordable than similarly priced gasoline vehicles.”

Source: https://electrek.co/2019/01/02/tesla-reduces-price-us-tax-credit-model-3/