每年有大量提交到USCIS的H-1B申请都是“E-V-C”模式的申请，英文中称该模式为Employer-Vendor-Client，中文称之为第三方场所工作模式。一般是小公司招员工时会这样帮员工申请签证。但是该雇主不直接提供实际工作给H-1b员工。通常小公司会为更大的公司提供员工，（大公司成为preferred vendor），大公司才是为员工提供实际工作的地方（称为最终客户）。偶尔这其中会有多个中间商。
因此如您所见，这种情况下实际雇主基本无法控制H-1B员工的项目跟进，绩效考核，以及其他正常雇主可控的关于该员工的因素。根据2010年USCIS发表的 H-1B 雇主-雇员关系备忘录，雇主和雇员的关系实际存在对于雇员的H-1B申请是必要的。也就是说明，该雇主需要保留对H-1B雇员工作的掌控权，然而明显在这种模式下很难完成。
示范
为了证明雇主雇员关系和掌控权实际存在，H-1B 雇主-雇员关系备忘录提供了一份非详尽清单可供雇主提交。这些包括类似大雇主（最终客户）和客户的劳动协议。在此备忘录中一个很重要的文件叫做 “End Client Letter” （最终客户证明信）。
最终客户证明信内容
该信件中应该包括公司名头并且由最终客户的员工签名，该员工可以是经理、HR人员或任何公司授权人员。该信件应包含H-1B员工将履行的职责、客户地址，项目市场以及H-1B员工需要和谁汇报。此外，该信件应说明H-1B员工愿意将掌控权交由给雇主，并且不会成为最终客户的雇员。
该信件是员工向USCIS申请签证时的必要文件，同时在美国使领馆获得H-1B签证时也需要提交该信件。
没有最终客户证明信
在EVC模式下也有即使没有最终客户证明信签证也顺利通过的例子。然而，H-1B雇员需要提供相当的文件和说服力极强的法律文件来证明雇员雇主关系是真实存在的，且雇主保持H-1B员工的控制权。雇主很可能会收到RFE通知（补件通知）。被拒绝的风险也相应更高。
H-1B最终客户证明信范例
[TO BE PRINTED ON END-CLIENT LETTERHEAD]
Re: End Client Letter for Mr. <EMPLOYEE NAME>
Dear Sir or Madam,
This letter serves to confirm that <CLIENT NAME> has a contract with <VENDOR NAME> to provide us with IT services including computer programming, systems analysis, web development, quality analysis, systems administration, and engineering services at our office located at <CLIENT ADDRESS>.
<EMPLOYEE NAME> of <EMPLOYER NAME> will performing the work at a Software Engineer on a project for <CLIENT NAME> at <CLIENT ADRESS>.
<EMPLOYEE NAME> will work on a project called <PROJECT NAME>, and as part of his assignment on this project, his primary job responsibilities will include:
- Analysis, design, and development of the <PROJECT NAME>
- Maintenance and enhancement of the functionality of the <PROJECT NAME>
- As part of <PROJECT NAME>, <EMPLOYEE NAME> will be developing web applications using Core Java, Spring, Hibernate, MySQL, REST, and SOAP API, as well as writing the unit test cases
- Interaction with the managers to gather the functional requirements
- Documenting the design and architecture and keeping the specification documents up to date
- Ensure that the systems are developed and deployed according to the functional requirements
A bachelor’s degree or equivalent work experience in Computer Science, Computer Information Systems, Electrical Engineering, Computer Engineering, Mathematics, or a related field is required as minimum education, training, and experience to perform the above job duties. <EMPLOYEE NAME> will work with peers and supervisors who will hold a bachelor’s degree or equivalent.
The duration of the project is expected to be at least through Nov 2, 2022, and is ongoing in duration subject to continuing business necessity, satisfactory performance, as well as continued agreement between <VENDOR NAME> and <CLIENT NAME> as well as between <VENDOR NAME> and <EMPLOYER NAME>.
<EMPLOYEE NAME> will work on a full-time basis (40 hours a week) and will be paid directly by his H-1B employer <EMPLOYER NAME> with regular salary, as well as get benefits in accordance with their company policies. <EMPLOYEE NAME> is not an employee of <CLIENT NAME>, and <CLIENT NAME> will not have the right to assign <EMPLOYEE NAME> to another project, location, or company as part of this assignment or project. <EMPLOYER NAME> will retain the full control of <EMPLOYEE NAME> for management, performance evaluation, assignment of duties, supervision, and hiring and firing decisions.
If you have further questions or need any clarifications, please feel free to contact me at any time.
Sincerely,
<AUTHORIZED PERSON NAME>
<CLIENT NAME>
Phone: <PHONE NUMBER>
Email: <EMAIL ADDRESS>
