The Internal Revenue Service alerted tax professionals Tuesday that over the next five weeks, it will send letters to some users of its online e-Services products informing them they will either have to go online or call the e-Services e-Help Desk to validate their identities, as part of the IRS’s battle against identity theft.

The letters will go to those e-Services users who can access the IRS’s Transcript Delivery Service and who have been active within the past year, the IRS noted. The IRS restored the online Get Transcript service this year with improved authentication procedures after taking it down last year once it discovered that identity thieves had used it to access hundreds of thousands of tax returns.

To find out more about which tax professionals are affected by the letters, who needs to validate their identities and what information is required, the IRS is directing users to the main e-Services page on its website, www.irs.gov/eservices.

Users who receive the letters from the IRS will then have 30 days either to authenticate their identities online or call the IRS to authenticate their IDs by phone.

Tax professionals should not call the e-Help Desk unless they receive a letter or their account gets suspended. However, if they do not revalidate their identities in time, the IRS warned their accounts will be suspended for security purposes.

The identity validation push is being prompted by the IRS’s continuing battle against hackers and identity thieves who have been employing increasingly sophisticated means to gain access to taxpayer identities, including by targeting tax preparers.

“Cybercriminals currently are engaged in ongoing phishing attempts to steal e-Services users’ usernames and passwords,” the IRS warned. “Be alert to phishing scams either by letter, email or phone. Make sure the communication you receive is from official IRS sources. If in doubt, go directly to IRS.gov.”