A report released Thursday by a workers’ advocacy group says Walmart, the nation’s largest private employer, routinely refuses to accept doctors’ notes, penalizes workers who need to take care of a sick family member and otherwise punishes employees for lawful absences.

The report, based on a survey of more than 1,000 employees, accuses Walmart of violating the Americans with Disabilities Act and the Family and Medical Leave Act, among other worker-protection laws. The group argued in a lawsuit filed last month, and in an earlier complaint with the Equal Employment Opportunity Commission, that Walmart discriminated against pregnant workers.

“Walmart should fully comply with the law so that no one is illegally punished for a disability-related absence or for taking care of themselves or a loved one with a serious medical condition,” said Dina Bakst, a founder and president of A Better Balance, the advocacy group that prepared the report.

Walmart said that it had not reviewed the report but disputed the group’s conclusions, and said that the company’s attendance policies helped make sure that there were enough employees to help customers while protecting workers from regularly covering others’ duties.

“We understand that associates may have to miss work on occasion, and we have processes in place to assist them,” Randy Hargrove, a spokesman for Walmart, said. The company reviews each employee’s circumstances individually, he said, “in compliance with company policy and the law.”

Katie Orzehowski says her miscarriage last fall almost cost her a job.

A cashier at the Walmart in North Huntingdon, Pa., Ms. Orzehowski said she tried to use doctors’ notes and hospitalization records to excuse her missed shifts, to no avail. Worried that another absence would get her fired, she went back to work.

“I still had a lot of bleeding going on, and that’s embarrassing,” Ms. Orzehowski, 26, said.

Her account is one of dozens included in the report, which clashes with the company’s recent efforts to project a more worker-friendly image.

Walmart has long been known for its penny-pinching attention to detail and its opposition to organized labor. But in the past couple of years, the company has announced that it would raise its minimum wage to $10 an hour and has pledged to invest heavily in training and paying workers.

Workers’ advocates have expressed skepticism about the retailer’s commitment to improving the lives of its more than one million employees. Around the same time that Walmart lifted wages, it cut merit raises and introduced a training program that could keep hourly pay at $9 an hour for up to 18 months.

In November, A Better Balance filed a complaint with the employment commission on behalf of Arleja Stevens, a Walmart employee who said she was fired after missing too many shifts because of complications from her pregnancy.

In that filing, the group accused Walmart of violating the Americans with Disabilities Act and the Pregnancy Discrimination Act. The employment commission is investigating the accusation, Ms. Bakst said.

Mr. Hargrove said the company disagreed with Ms. Stevens’s claims.

A Better Balance also participated in a separate lawsuit last month alleging that Walmart discriminated against pregnant employees

The company has disputed the claims of the two women at the center of the suit. Autocad 2012 license key.

A Better Balance wrote the survey questions used for Thursday’s report. The questions asked employees whether they believed that Walmart had a problem of regularly punishing people for absences relating to an illness or disability, and about how the company treated absences. The group worked with the labor group OUR Walmart, which promoted the survey to workers who listed Walmart as their employer on Facebook, according to Andrea Dehlendorf, a director of OUR Walmart.

“Although this system is supposed to be ‘neutral’ and punish all absences equally, along the lines of a ‘three-strikes-and-you’re-out’ policy, in reality, such a system is brutally unfair,” the report says of Walmart’s absence-control policy. “It punishes workers for things they cannot control and disproportionately harms the most vulnerable workers.”

Walmart assigns disciplinary points for unexcused absences and other infractions. Nine points in a six-month period can result in an employee’s being fired, according to a copy of the company’s absence policy reviewed by The New York Times. New employees may be fired for accruing four points in their first six months.

While Walmart has written guidelines for how managers and supervisors should respond to employees who need help because of medical issues, those policies are not always followed, according to the report.

“They just straight up tell you, ‘We don’t accept excuses,’” said Ms. Orzehowski, who still works for the company.

In a follow-up email, Mr. Hargrove said that the company did “not have any information that would support that Ms. Orzehowski advised us of a medical reason for her absences.”

“If that were the case, she could have used those medical records to apply for a leave or accommodation,” he said.

The Americans with Disabilities Act requires businesses with 15 or more employees to make reasonable accommodations for disabled workers. In 2008, the definition of a disabled worker was expanded, to include temporary medical conditions like complications relating to a pregnancy.

The Family and Medical Leave Act protects eligible workers — those who have been employed for 12 months at a company with 50 or more employees — who need to take time off to care for themselves or a family member.

Under the A.D.A., employers must work with employees to determine if workers are eligible for such accommodations. Dismissing doctors’ notes or otherwise refusing to consider the reason for a worker’s absence could potentially be “skirting the analysis” in which employers are required to engage, according to Michelle Caiola, the director of litigation for Disability Rights Advocates, a nonprofit group, and a former senior trial lawyer for the E.E.O.C., which enforces federal worker protections.

“A company as big as Walmart, it’s surprising that they don’t have the appropriate training for the personnel that would be overseeing these sorts of leaves,” Ms. Caiola said.

Mr. Hargrove said that the company had worked with “countless” employees to successfully authorize their absences from work.