Small businesses continue to struggle gaining capital, a new survey by the National Small Business Association (NSBA) found. A large minority have been unable to find financing over the past few years, while a smaller but significant number of business owners who obtained financing have seen the terms tighten or their loans or lines of credit called in early by their lenders.

The survey, done in May, includes responses from 300 small business members of the NSBA. Ninety percent have between one and 99 employees.

Almost half the respondents -- 43 percent -- indicated that they needed funds for their businesses over the past four years, but were unable to find a lender. One-fourth said they were turned down due to insufficient collateral, while one-fifth were declined due to a low credit score.

As if tight financing weren't enough, businesses are being squeezed on the other side as well. More than one in five respondents indicated that clients are taking longer to pay.

Although just over one-third said that the lack of capital didn't have an effect on their companies, 53 percent said they'd been unable to grow their business or expand operations. Nearly one-third had to reduce their employee roster, while one-fourth were unable to finance sales growth.

Even the companies that were able to obtain financing haven't had that easy of a go of it. Nearly one-third, or 29 percent, saw their credit lines reduced, while 9 percent had their loan called in early by their lender. When this occurred, 80 percent had no more than 60 days to comply; 19 percent had less than 15 days. Given that the average credit line balance across respondents topped $250,000, a bank's decision to call it early could be devastating.

Perhaps not surprisingly, just over one-fourth of respondents changed banks in the last four years. The top reasons for making the switch: feeling mistreated by their previous bank, obtaining better financing terms from a different bank, or simply wanting to work with a smaller bank.

Indeed, small banks garnered the largest number of high marks on service from small business owners. Nearly three-fourths said their service was good or excellent, versus 47 percent that said the same for large banks.

Large banks remain a financing mainstay for small businesses, however. Sixty percent report working with one, versus 47 percent that patronize small community banks. One-third have financed via credit cards, and only 11 percent through credit unions.

Small business owners may want to re-think this, given the findings not only from the NSBA, but also from the latest Biz2Credit Small Business Lending Index. During May, 2012, banks with more than $10 billion in assets approved little more than 10 percent of the loan applications submitted to them, while small banks gave a thumbs up to 46 percent of applicants. Credit unions topped even small banks, however, approving nearly 58 percent of loan applications. Biz2Credit is a credit marketplace.