Markit's flash reading of the US services purchasing manager's index was 55.6 for September, in line with expectations.
In August, the index was 56.1.
According to the release, some business owners became less confident in the economic outlook and so were reluctant to take on new projects.
The report also noted that the pace of business activity growth slowed to a three-month low. Average prices fell for a second straight month.
Relative to the manufacturing sector, the services industry been much stronger.
Markit chief economist Chris Williamson wrote, "Business optimism slumped to one of the lowest levels seen since the global financial crisis, inflows of new business rose at the weakest rate for eight months and job creation slipped to a six-month low. Growth is also becoming increasingly reliant on the services economy as manufacturers struggle against the strong dollar and weak demand in export markets."
