Always list them even if you had the job for a day say you kept it from 6/06-6/06
and if I'm not mistaken they usually just confirm your employment there, salary etc
http://www.privacyrights.org/fs/fs16-bck.htm#2
What can my former employer say about me?
Often a potential employer will contact an applicant's past employers. A former boss can say anything [truthful] about your performance. However, most employers have a policy to only confirm dates of employment, final salary, and other limited information. California law prohibits employers from intentionally interfering with former employees' attempts to find jobs by giving out false or misleading references. (California Labor Code §1050)
Under California law and the laws of many other states, employees have a right to review their own personnel files and make copies of documents they have signed. If you are a state or federal employee, your personnel file is protected under the California Information Practices Act or the federal Privacy Act of 1974 and can only be disclosed under limited circumstances. (California Civil Code §56.20; California Labor Code §§432, 1198.5; 5 USC §552a)
Jobs such as truck driver positions fall under regulations of the federal Department of Transportation. Employers are required to accurately respond to an inquiry from a prospective employer about whether you took a drug test, refused a drug test, or tested positive in a drug test with the former or current employer. (49 CFR §40.25, 49 CFR §382.413. Federal Motor Carrier Safety Administration Regulations)