The National Labor Relations Board plans to revisit its joint employer standard by this summer, this time using rulemaking procedures. NLRB Chairman John Ring confirmed the move in a letter on Tuesday to three US senators who had raised concerns over the process in their own letter last month.

While the NLRB previously announced the rulemaking plans, the letter laid out a timeline.

“A majority of the board is committed to engage in rulemaking, and the NLRB will do so,” Ring wrote. “Internal preparations are underway, and we are working toward issuance of a Notice of Proposed Rulemaking as soon as possible, but certainly by this summer.”

At issue is a 2015 NLRB decision that expanded the definition of who is a joint employer. In that case, the NLRB 3-2 vote that staffing firm workers at a Browning-Ferris Industries of California recycling site in Milpitas, Calif., were jointly employed by both BFI and the staffing firm. The expanded standard enabled unions to negotiate with both directly hired and staffing firm workers on the site.

Last December, a new NLRB tried to overturn the decision by using a test case, but that vote was vacated after it was found one board member should have recused himself.

In addition, Ring wrote in his letter that the NLRB would be in compliance with ethical obligations, also a concern raised by the senators.

US Sens. Ann Warren, Bernie Sanders and Kirsten Gillibrand issued their letter last month opposed to starting the rulemaking and raising concerns that reversing the 2015 decision would undermine labor rights clarified by the board’s 2015 vote.

“This 2015 ruling reaffirmed that, under the National Labor Relations Act, corporations with indirect control or reserved authority over workers can be held accountable for violating their rights,” according to the letter. “Last year, the board tried to reverse this ruling through a rushed adjudication process, but later vacated the reversal because the Inspector General and the board’s Designated Agency Ethics Official both determined that Member William Emanuel’s participation violated federal ethics rules.”

They also noted the 2015 decision is the subject of ongoing litigation in a federal appeals court and the board’s use of rulemaking may be to evade ethical restrictions.