Customers are showing early reluctance to support a merger between cell phone companies AT&T and T-Mobile, a customer survey showed Tuesday.

The report, compiled by the American Customer Service Satisfaction Index shows a decrease in customer satisfaction (scored between 0 and 100 points) for the merging companies, while customers have shown more faith in competitors Verizon and Sprint.

AT&T is the lowest rated of the four companies, with a score of 66, falling four points from last year. Verizon and Sprint have identical scores of 72, while T-Mobile, formerly the highest-rated company, fell four points to 70, its lowest rating in five years.

“It is common to find a reduction in customer satisfaction after mergers, but it is rare for customer satisfaction to drop ahead of a merger,” said ACSI founder Claes Fornell.

At&T has put forward a plan to buy Bellevue-based T-Mobile for $39 billion. The sale is likely to be put through the federal wringer because of a limited amount of wireless competition in the market.

The deal has received sharp criticism, and it will intensify competition at the top of the market between AT&T and Verizon. Customers have long enjoyed T-Mobile’s cheap plans and customer service, and it remains unclear how customers will react when they are brought in to the AT&T system.

“Assuming the deal is approved, it remains to be seen if a much larger AT&T can regain the strength of its customer relationships,” Fornell said.