This week saw the biggest staging date yet in the roll-out of auto-enrolment, with 10,700 employers due to sign up their workforces into a pension plan on July 1. The responsibilities hit firms with fewer than 50 staff next month.
Employees earning more than £10,000 a year will have to be enrolled into a pension unless they opt out.
Even among larger firms, of almost 23,000 which hit their staging date by May 1, close to 8,000 were yet to register by the end of May, though they have at most five months to catch up, according to The Pensions Regulator.
Kaith Khalaf, head of corporate research at Hargeaves Lansdown, said: "Perhaps many of them just haven't yet got around to it yet.
"Nevertheless, these numbers seem to be consistent with anecdotal feedback we're getting from within the industry that some employers in the current wave of staging are struggling to meet their obligations on time."
Sean McSweeney, at Chase de Vere, said: "Based on the number of employers contacting us for help very close to their staging date, we have real concerns thousands of employers are leaving it too late.
"These employers risk failing to meet their auto-enrolment deadlines or having to pay considerably greater costs to advisers and payroll providers to get them over the line at very short notice."
John Wilson, of JLT Employee Benefits in Edinburgh, said: "A lot of employers are just waking up to their auto-enrolment duties."
He said JLT had developed a more commoditised proposition where employers could choose what they wanted to do themselves and pay a fixed fee for anything else. "The regulator is beefing up a compliance team but the simple fact is whether by accident or design there will be a lot of non-compliance."
Graeme Forbes, at Glasgow-based financial planners Intelligent Capital, said 152,900 of the smallest UK employers would reach their staging date in 2015/16 and around 617,000 in the following tax year.
"On the basis Scotland accounts for around one in ten of the population, that amounts to a big headache for Scottish SMEs, which will all be rushing to set schemes up at the same time."
It raised questions about the capacity of the pensions industry advisory community, Mr Forbes said. "The biggest problem will be the burden of SMEs complying with all the regulations, record keeping and so on that will be required. Larger firms with dedicated HR departments and the scale to afford software packages will cope, but SMEs typically don't have the resources. The Pension Regulator has not been slow in fining firms who don't comply so this is not voluntary and could have significant implications."
Mr Forbes said his firm had negotiated access to a software package which relieved employers of the main burdens.
Mr McSweeney said: "As ever greater numbers of companies reach their staging dates this situation could become far worse. We need the message to sink in with employers that they cannot leave auto-enrolment planning to the very last minute."