ERISA is the federal law that spells out the rules regarding pension plans available to employees through their workplace. While ERISA does not generally regulate the content of plans, it does provide minimum standards for certain aspects of the plan such as how employees are informed about the pension plans, how plans should be funded, and how an employee's pension rights can become vested and therefore cannot be forfeited. ERISA also gives employees the right to sue the plan fiduciaries if they have wrongfully been denied benefits or if the plan fiduciaries have breached their fiduciary duty to plan participants.
Some common issues that employees encounter are miscalculation of benefits due to them under a pension plan or wrongful denial of benefits to which an employee is entitled. If you have been wrongfully denied benefits due to you because the plan has incorrectly determined you are not entitled to benefits, or has miscalculated the amount you are entitled to, you should speak to an attorney who specializes in ERISA who can guide you through what remedies may be available.
The Department of Labor has a wonderful resource for frequently asked questions at http://www.dol.gov/ebsa/faqs/faq_compliance_pension.html.