The antitrust trial that seeks to halt the merger of JetBlue and Spirit Airlines has begun in Boston. The merger has faced opposition from the United States Department of Justice (DOJ) and several states due to concerns about limited choices and higher ticket prices. The trial is expected to last about a month.

JetBlue hopes to create a national low-fare competitor to the “Big Four” carriers through its proposed $3.8 billion acquisition of Spirit. The DOJ filed suit in March when Attorney General Merrick Garland said the merger would hurt “tens of millions of travelers, with the greatest impact felt by those who rely on what are known as ultra-low-cost carriers in order to fly.”

Garland added that the DOJ has obtained internal communications showing JetBlue’s intention to eliminate Spirit’s disruptive business model, which forced other airlines to lower prices for the same routes.

An additional four states joined the lawsuit at the end of March.

Earlier this year, the DOJ successfully won a separate case against JetBlue and American Airlines, which resulted in a court ordering the companies to dissolve an alliance. In that case, the government argued that their consolidation harmed air travelers by eliminating competition in a highly concentrated market.